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freebsd-nq/sys/kern/subr_witness.c
Enji Cooper d6701b6c8c Add kern.features.witness 
Adding `kern.features.witness` helps expose whether or not the kernel has
`options WITNESS` enabled, so the `feature_present(3)` API can be used
to query whether or not witness(9) is built into the kernel.

This support is helpful with userspace applications (generally speaking,
tests), as it can be queried to determine whether or not tests related
to WITNESS should be run.

MFC after:	1 week
Reviewed by: cem, darrick.freebsd_gmail.com
Differential Revision: https://reviews.freebsd.org/D25302
Sponsored by:	DellEMC Isilon
2020-06-24 18:51:01 +00:00

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/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 2008 Isilon Systems, Inc.
* Copyright (c) 2008 Ilya Maykov <ivmaykov@gmail.com>
* Copyright (c) 1998 Berkeley Software Design, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Berkeley Software Design Inc's name may not be used to endorse or
* promote products derived from this software without specific prior
* written permission.
*
* THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
* and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
*/
/*
* Implementation of the `witness' lock verifier. Originally implemented for
* mutexes in BSD/OS. Extended to handle generic lock objects and lock
* classes in FreeBSD.
*/
/*
* Main Entry: witness
* Pronunciation: 'wit-n&s
* Function: noun
* Etymology: Middle English witnesse, from Old English witnes knowledge,
* testimony, witness, from 2wit
* Date: before 12th century
* 1 : attestation of a fact or event : TESTIMONY
* 2 : one that gives evidence; specifically : one who testifies in
* a cause or before a judicial tribunal
* 3 : one asked to be present at a transaction so as to be able to
* testify to its having taken place
* 4 : one who has personal knowledge of something
* 5 a : something serving as evidence or proof : SIGN
* b : public affirmation by word or example of usually
* religious faith or conviction <the heroic witness to divine
* life -- Pilot>
* 6 capitalized : a member of the Jehovah's Witnesses
*/
/*
* Special rules concerning Giant and lock orders:
*
* 1) Giant must be acquired before any other mutexes. Stated another way,
* no other mutex may be held when Giant is acquired.
*
* 2) Giant must be released when blocking on a sleepable lock.
*
* This rule is less obvious, but is a result of Giant providing the same
* semantics as spl(). Basically, when a thread sleeps, it must release
* Giant. When a thread blocks on a sleepable lock, it sleeps. Hence rule
* 2).
*
* 3) Giant may be acquired before or after sleepable locks.
*
* This rule is also not quite as obvious. Giant may be acquired after
* a sleepable lock because it is a non-sleepable lock and non-sleepable
* locks may always be acquired while holding a sleepable lock. The second
* case, Giant before a sleepable lock, follows from rule 2) above. Suppose
* you have two threads T1 and T2 and a sleepable lock X. Suppose that T1
* acquires X and blocks on Giant. Then suppose that T2 acquires Giant and
* blocks on X. When T2 blocks on X, T2 will release Giant allowing T1 to
* execute. Thus, acquiring Giant both before and after a sleepable lock
* will not result in a lock order reversal.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_ddb.h"
#include "opt_hwpmc_hooks.h"
#include "opt_stack.h"
#include "opt_witness.h"
#include <sys/param.h>
#include <sys/bus.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/sched.h>
#include <sys/stack.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#ifdef DDB
#include <ddb/ddb.h>
#endif
#include <machine/stdarg.h>
#if !defined(DDB) && !defined(STACK)
#error "DDB or STACK options are required for WITNESS"
#endif
/* Note that these traces do not work with KTR_ALQ. */
#if 0
#define KTR_WITNESS KTR_SUBSYS
#else
#define KTR_WITNESS 0
#endif
#define LI_RECURSEMASK 0x0000ffff /* Recursion depth of lock instance. */
#define LI_EXCLUSIVE 0x00010000 /* Exclusive lock instance. */
#define LI_NORELEASE 0x00020000 /* Lock not allowed to be released. */
#define LI_SLEEPABLE 0x00040000 /* Lock may be held while sleeping. */
#ifndef WITNESS_COUNT
#define WITNESS_COUNT 1536
#endif
#define WITNESS_HASH_SIZE 251 /* Prime, gives load factor < 2 */
#define WITNESS_PENDLIST (512 + (MAXCPU * 4))
/* Allocate 256 KB of stack data space */
#define WITNESS_LO_DATA_COUNT 2048
/* Prime, gives load factor of ~2 at full load */
#define WITNESS_LO_HASH_SIZE 1021
/*
* XXX: This is somewhat bogus, as we assume here that at most 2048 threads
* will hold LOCK_NCHILDREN locks. We handle failure ok, and we should
* probably be safe for the most part, but it's still a SWAG.
*/
#define LOCK_NCHILDREN 5
#define LOCK_CHILDCOUNT 2048
#define MAX_W_NAME 64
#define FULLGRAPH_SBUF_SIZE 512
/*
* These flags go in the witness relationship matrix and describe the
* relationship between any two struct witness objects.
*/
#define WITNESS_UNRELATED 0x00 /* No lock order relation. */
#define WITNESS_PARENT 0x01 /* Parent, aka direct ancestor. */
#define WITNESS_ANCESTOR 0x02 /* Direct or indirect ancestor. */
#define WITNESS_CHILD 0x04 /* Child, aka direct descendant. */
#define WITNESS_DESCENDANT 0x08 /* Direct or indirect descendant. */
#define WITNESS_ANCESTOR_MASK (WITNESS_PARENT | WITNESS_ANCESTOR)
#define WITNESS_DESCENDANT_MASK (WITNESS_CHILD | WITNESS_DESCENDANT)
#define WITNESS_RELATED_MASK \
(WITNESS_ANCESTOR_MASK | WITNESS_DESCENDANT_MASK)
#define WITNESS_REVERSAL 0x10 /* A lock order reversal has been
* observed. */
#define WITNESS_RESERVED1 0x20 /* Unused flag, reserved. */
#define WITNESS_RESERVED2 0x40 /* Unused flag, reserved. */
#define WITNESS_LOCK_ORDER_KNOWN 0x80 /* This lock order is known. */
/* Descendant to ancestor flags */
#define WITNESS_DTOA(x) (((x) & WITNESS_RELATED_MASK) >> 2)
/* Ancestor to descendant flags */
#define WITNESS_ATOD(x) (((x) & WITNESS_RELATED_MASK) << 2)
#define WITNESS_INDEX_ASSERT(i) \
MPASS((i) > 0 && (i) <= w_max_used_index && (i) < witness_count)
static MALLOC_DEFINE(M_WITNESS, "Witness", "Witness");
/*
* Lock instances. A lock instance is the data associated with a lock while
* it is held by witness. For example, a lock instance will hold the
* recursion count of a lock. Lock instances are held in lists. Spin locks
* are held in a per-cpu list while sleep locks are held in per-thread list.
*/
struct lock_instance {
struct lock_object *li_lock;
const char *li_file;
int li_line;
u_int li_flags;
};
/*
* A simple list type used to build the list of locks held by a thread
* or CPU. We can't simply embed the list in struct lock_object since a
* lock may be held by more than one thread if it is a shared lock. Locks
* are added to the head of the list, so we fill up each list entry from
* "the back" logically. To ease some of the arithmetic, we actually fill
* in each list entry the normal way (children[0] then children[1], etc.) but
* when we traverse the list we read children[count-1] as the first entry
* down to children[0] as the final entry.
*/
struct lock_list_entry {
struct lock_list_entry *ll_next;
struct lock_instance ll_children[LOCK_NCHILDREN];
u_int ll_count;
};
/*
* The main witness structure. One of these per named lock type in the system
* (for example, "vnode interlock").
*/
struct witness {
char w_name[MAX_W_NAME];
uint32_t w_index; /* Index in the relationship matrix */
struct lock_class *w_class;
STAILQ_ENTRY(witness) w_list; /* List of all witnesses. */
STAILQ_ENTRY(witness) w_typelist; /* Witnesses of a type. */
struct witness *w_hash_next; /* Linked list in hash buckets. */
const char *w_file; /* File where last acquired */
uint32_t w_line; /* Line where last acquired */
uint32_t w_refcount;
uint16_t w_num_ancestors; /* direct/indirect
* ancestor count */
uint16_t w_num_descendants; /* direct/indirect
* descendant count */
int16_t w_ddb_level;
unsigned w_displayed:1;
unsigned w_reversed:1;
};
STAILQ_HEAD(witness_list, witness);
/*
* The witness hash table. Keys are witness names (const char *), elements are
* witness objects (struct witness *).
*/
struct witness_hash {
struct witness *wh_array[WITNESS_HASH_SIZE];
uint32_t wh_size;
uint32_t wh_count;
};
/*
* Key type for the lock order data hash table.
*/
struct witness_lock_order_key {
uint16_t from;
uint16_t to;
};
struct witness_lock_order_data {
struct stack wlod_stack;
struct witness_lock_order_key wlod_key;
struct witness_lock_order_data *wlod_next;
};
/*
* The witness lock order data hash table. Keys are witness index tuples
* (struct witness_lock_order_key), elements are lock order data objects
* (struct witness_lock_order_data).
*/
struct witness_lock_order_hash {
struct witness_lock_order_data *wloh_array[WITNESS_LO_HASH_SIZE];
u_int wloh_size;
u_int wloh_count;
};
struct witness_blessed {
const char *b_lock1;
const char *b_lock2;
};
struct witness_pendhelp {
const char *wh_type;
struct lock_object *wh_lock;
};
struct witness_order_list_entry {
const char *w_name;
struct lock_class *w_class;
};
/*
* Returns 0 if one of the locks is a spin lock and the other is not.
* Returns 1 otherwise.
*/
static __inline int
witness_lock_type_equal(struct witness *w1, struct witness *w2)
{
return ((w1->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)) ==
(w2->w_class->lc_flags & (LC_SLEEPLOCK | LC_SPINLOCK)));
}
static __inline int
witness_lock_order_key_equal(const struct witness_lock_order_key *a,
const struct witness_lock_order_key *b)
{
return (a->from == b->from && a->to == b->to);
}
static int _isitmyx(struct witness *w1, struct witness *w2, int rmask,
const char *fname);
static void adopt(struct witness *parent, struct witness *child);
static int blessed(struct witness *, struct witness *);
static void depart(struct witness *w);
static struct witness *enroll(const char *description,
struct lock_class *lock_class);
static struct lock_instance *find_instance(struct lock_list_entry *list,
const struct lock_object *lock);
static int isitmychild(struct witness *parent, struct witness *child);
static int isitmydescendant(struct witness *parent, struct witness *child);
static void itismychild(struct witness *parent, struct witness *child);
static int sysctl_debug_witness_badstacks(SYSCTL_HANDLER_ARGS);
static int sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS);
static int sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS);
static int sysctl_debug_witness_channel(SYSCTL_HANDLER_ARGS);
static void witness_add_fullgraph(struct sbuf *sb, struct witness *parent);
#ifdef DDB
static void witness_ddb_compute_levels(void);
static void witness_ddb_display(int(*)(const char *fmt, ...));
static void witness_ddb_display_descendants(int(*)(const char *fmt, ...),
struct witness *, int indent);
static void witness_ddb_display_list(int(*prnt)(const char *fmt, ...),
struct witness_list *list);
static void witness_ddb_level_descendants(struct witness *parent, int l);
static void witness_ddb_list(struct thread *td);
#endif
static void witness_debugger(int cond, const char *msg);
static void witness_free(struct witness *m);
static struct witness *witness_get(void);
static uint32_t witness_hash_djb2(const uint8_t *key, uint32_t size);
static struct witness *witness_hash_get(const char *key);
static void witness_hash_put(struct witness *w);
static void witness_init_hash_tables(void);
static void witness_increment_graph_generation(void);
static void witness_lock_list_free(struct lock_list_entry *lle);
static struct lock_list_entry *witness_lock_list_get(void);
static int witness_lock_order_add(struct witness *parent,
struct witness *child);
static int witness_lock_order_check(struct witness *parent,
struct witness *child);
static struct witness_lock_order_data *witness_lock_order_get(
struct witness *parent,
struct witness *child);
static void witness_list_lock(struct lock_instance *instance,
int (*prnt)(const char *fmt, ...));
static int witness_output(const char *fmt, ...) __printflike(1, 2);
static int witness_voutput(const char *fmt, va_list ap) __printflike(1, 0);
static void witness_setflag(struct lock_object *lock, int flag, int set);
FEATURE(witness, "kernel has witness(9) support");
static SYSCTL_NODE(_debug, OID_AUTO, witness, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
"Witness Locking");
/*
* If set to 0, lock order checking is disabled. If set to -1,
* witness is completely disabled. Otherwise witness performs full
* lock order checking for all locks. At runtime, lock order checking
* may be toggled. However, witness cannot be reenabled once it is
* completely disabled.
*/
static int witness_watch = 1;
SYSCTL_PROC(_debug_witness, OID_AUTO, watch,
CTLFLAG_RWTUN | CTLTYPE_INT | CTLFLAG_MPSAFE, NULL, 0,
sysctl_debug_witness_watch, "I",
"witness is watching lock operations");
#ifdef KDB
/*
* When KDB is enabled and witness_kdb is 1, it will cause the system
* to drop into kdebug() when:
* - a lock hierarchy violation occurs
* - locks are held when going to sleep.
*/
#ifdef WITNESS_KDB
int witness_kdb = 1;
#else
int witness_kdb = 0;
#endif
SYSCTL_INT(_debug_witness, OID_AUTO, kdb, CTLFLAG_RWTUN, &witness_kdb, 0, "");
#endif /* KDB */
#if defined(DDB) || defined(KDB)
/*
* When DDB or KDB is enabled and witness_trace is 1, it will cause the system
* to print a stack trace:
* - a lock hierarchy violation occurs
* - locks are held when going to sleep.
*/
int witness_trace = 1;
SYSCTL_INT(_debug_witness, OID_AUTO, trace, CTLFLAG_RWTUN, &witness_trace, 0, "");
#endif /* DDB || KDB */
#ifdef WITNESS_SKIPSPIN
int witness_skipspin = 1;
#else
int witness_skipspin = 0;
#endif
SYSCTL_INT(_debug_witness, OID_AUTO, skipspin, CTLFLAG_RDTUN, &witness_skipspin, 0, "");
int badstack_sbuf_size;
int witness_count = WITNESS_COUNT;
SYSCTL_INT(_debug_witness, OID_AUTO, witness_count, CTLFLAG_RDTUN,
&witness_count, 0, "");
/*
* Output channel for witness messages. By default we print to the console.
*/
enum witness_channel {
WITNESS_CONSOLE,
WITNESS_LOG,
WITNESS_NONE,
};
static enum witness_channel witness_channel = WITNESS_CONSOLE;
SYSCTL_PROC(_debug_witness, OID_AUTO, output_channel,
CTLTYPE_STRING | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, NULL, 0,
sysctl_debug_witness_channel, "A",
"Output channel for warnings");
/*
* Call this to print out the relations between locks.
*/
SYSCTL_PROC(_debug_witness, OID_AUTO, fullgraph,
CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
sysctl_debug_witness_fullgraph, "A",
"Show locks relation graphs");
/*
* Call this to print out the witness faulty stacks.
*/
SYSCTL_PROC(_debug_witness, OID_AUTO, badstacks,
CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE, NULL, 0,
sysctl_debug_witness_badstacks, "A",
"Show bad witness stacks");
static struct mtx w_mtx;
/* w_list */
static struct witness_list w_free = STAILQ_HEAD_INITIALIZER(w_free);
static struct witness_list w_all = STAILQ_HEAD_INITIALIZER(w_all);
/* w_typelist */
static struct witness_list w_spin = STAILQ_HEAD_INITIALIZER(w_spin);
static struct witness_list w_sleep = STAILQ_HEAD_INITIALIZER(w_sleep);
/* lock list */
static struct lock_list_entry *w_lock_list_free = NULL;
static struct witness_pendhelp pending_locks[WITNESS_PENDLIST];
static u_int pending_cnt;
static int w_free_cnt, w_spin_cnt, w_sleep_cnt;
SYSCTL_INT(_debug_witness, OID_AUTO, free_cnt, CTLFLAG_RD, &w_free_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, spin_cnt, CTLFLAG_RD, &w_spin_cnt, 0, "");
SYSCTL_INT(_debug_witness, OID_AUTO, sleep_cnt, CTLFLAG_RD, &w_sleep_cnt, 0,
"");
static struct witness *w_data;
static uint8_t **w_rmatrix;
static struct lock_list_entry w_locklistdata[LOCK_CHILDCOUNT];
static struct witness_hash w_hash; /* The witness hash table. */
/* The lock order data hash */
static struct witness_lock_order_data w_lodata[WITNESS_LO_DATA_COUNT];
static struct witness_lock_order_data *w_lofree = NULL;
static struct witness_lock_order_hash w_lohash;
static int w_max_used_index = 0;
static unsigned int w_generation = 0;
static const char w_notrunning[] = "Witness not running\n";
static const char w_stillcold[] = "Witness is still cold\n";
#ifdef __i386__
static const char w_notallowed[] = "The sysctl is disabled on the arch\n";
#endif
static struct witness_order_list_entry order_lists[] = {
/*
* sx locks
*/
{ "proctree", &lock_class_sx },
{ "allproc", &lock_class_sx },
{ "allprison", &lock_class_sx },
{ NULL, NULL },
/*
* Various mutexes
*/
{ "Giant", &lock_class_mtx_sleep },
{ "pipe mutex", &lock_class_mtx_sleep },
{ "sigio lock", &lock_class_mtx_sleep },
{ "process group", &lock_class_mtx_sleep },
#ifdef HWPMC_HOOKS
{ "pmc-sleep", &lock_class_mtx_sleep },
#endif
{ "process lock", &lock_class_mtx_sleep },
{ "session", &lock_class_mtx_sleep },
{ "uidinfo hash", &lock_class_rw },
{ "time lock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* umtx
*/
{ "umtx lock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* Sockets
*/
{ "accept", &lock_class_mtx_sleep },
{ "so_snd", &lock_class_mtx_sleep },
{ "so_rcv", &lock_class_mtx_sleep },
{ "sellck", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* Routing
*/
{ "so_rcv", &lock_class_mtx_sleep },
{ "radix node head", &lock_class_rm },
{ "rtentry", &lock_class_mtx_sleep },
{ "ifaddr", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* IPv4 multicast:
* protocol locks before interface locks, after UDP locks.
*/
{ "in_multi_sx", &lock_class_sx },
{ "udpinp", &lock_class_rw },
{ "in_multi_list_mtx", &lock_class_mtx_sleep },
{ "igmp_mtx", &lock_class_mtx_sleep },
{ "ifnet_rw", &lock_class_rw },
{ "if_addr_lock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* IPv6 multicast:
* protocol locks before interface locks, after UDP locks.
*/
{ "in6_multi_sx", &lock_class_sx },
{ "udpinp", &lock_class_rw },
{ "in6_multi_list_mtx", &lock_class_mtx_sleep },
{ "mld_mtx", &lock_class_mtx_sleep },
{ "ifnet_rw", &lock_class_rw },
{ "if_addr_lock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* UNIX Domain Sockets
*/
{ "unp_link_rwlock", &lock_class_rw },
{ "unp_list_lock", &lock_class_mtx_sleep },
{ "unp", &lock_class_mtx_sleep },
{ "so_snd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* UDP/IP
*/
{ "udp", &lock_class_mtx_sleep },
{ "udpinp", &lock_class_rw },
{ "so_snd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* TCP/IP
*/
{ "tcp", &lock_class_mtx_sleep },
{ "tcpinp", &lock_class_rw },
{ "so_snd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* BPF
*/
{ "bpf global lock", &lock_class_sx },
{ "bpf cdev lock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* NFS server
*/
{ "nfsd_mtx", &lock_class_mtx_sleep },
{ "so_snd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* IEEE 802.11
*/
{ "802.11 com lock", &lock_class_mtx_sleep},
{ NULL, NULL },
/*
* Network drivers
*/
{ "network driver", &lock_class_mtx_sleep},
{ NULL, NULL },
/*
* Netgraph
*/
{ "ng_node", &lock_class_mtx_sleep },
{ "ng_worklist", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* CDEV
*/
{ "vm map (system)", &lock_class_mtx_sleep },
{ "vnode interlock", &lock_class_mtx_sleep },
{ "cdev", &lock_class_mtx_sleep },
{ "devthrd", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* VM
*/
{ "vm map (user)", &lock_class_sx },
{ "vm object", &lock_class_rw },
{ "vm page", &lock_class_mtx_sleep },
{ "pmap pv global", &lock_class_rw },
{ "pmap", &lock_class_mtx_sleep },
{ "pmap pv list", &lock_class_rw },
{ "vm page free queue", &lock_class_mtx_sleep },
{ "vm pagequeue", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* kqueue/VFS interaction
*/
{ "kqueue", &lock_class_mtx_sleep },
{ "struct mount mtx", &lock_class_mtx_sleep },
{ "vnode interlock", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* VFS namecache
*/
{ "ncvn", &lock_class_mtx_sleep },
{ "ncbuc", &lock_class_rw },
{ "vnode interlock", &lock_class_mtx_sleep },
{ "ncneg", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* ZFS locking
*/
{ "dn->dn_mtx", &lock_class_sx },
{ "dr->dt.di.dr_mtx", &lock_class_sx },
{ "db->db_mtx", &lock_class_sx },
{ NULL, NULL },
/*
* TCP log locks
*/
{ "TCP ID tree", &lock_class_rw },
{ "tcp log id bucket", &lock_class_mtx_sleep },
{ "tcpinp", &lock_class_rw },
{ "TCP log expireq", &lock_class_mtx_sleep },
{ NULL, NULL },
/*
* spin locks
*/
#ifdef SMP
{ "ap boot", &lock_class_mtx_spin },
#endif
{ "rm.mutex_mtx", &lock_class_mtx_spin },
{ "sio", &lock_class_mtx_spin },
#ifdef __i386__
{ "cy", &lock_class_mtx_spin },
#endif
{ "scc_hwmtx", &lock_class_mtx_spin },
{ "uart_hwmtx", &lock_class_mtx_spin },
{ "fast_taskqueue", &lock_class_mtx_spin },
{ "intr table", &lock_class_mtx_spin },
{ "process slock", &lock_class_mtx_spin },
{ "syscons video lock", &lock_class_mtx_spin },
{ "sleepq chain", &lock_class_mtx_spin },
{ "rm_spinlock", &lock_class_mtx_spin },
{ "turnstile chain", &lock_class_mtx_spin },
{ "turnstile lock", &lock_class_mtx_spin },
{ "sched lock", &lock_class_mtx_spin },
{ "td_contested", &lock_class_mtx_spin },
{ "callout", &lock_class_mtx_spin },
{ "entropy harvest mutex", &lock_class_mtx_spin },
#ifdef SMP
{ "smp rendezvous", &lock_class_mtx_spin },
#endif
#ifdef __powerpc__
{ "tlb0", &lock_class_mtx_spin },
#endif
{ NULL, NULL },
{ "sched lock", &lock_class_mtx_spin },
#ifdef HWPMC_HOOKS
{ "pmc-per-proc", &lock_class_mtx_spin },
#endif
{ NULL, NULL },
/*
* leaf locks
*/
{ "intrcnt", &lock_class_mtx_spin },
{ "icu", &lock_class_mtx_spin },
#ifdef __i386__
{ "allpmaps", &lock_class_mtx_spin },
{ "descriptor tables", &lock_class_mtx_spin },
#endif
{ "clk", &lock_class_mtx_spin },
{ "cpuset", &lock_class_mtx_spin },
{ "mprof lock", &lock_class_mtx_spin },
{ "zombie lock", &lock_class_mtx_spin },
{ "ALD Queue", &lock_class_mtx_spin },
#if defined(__i386__) || defined(__amd64__)
{ "pcicfg", &lock_class_mtx_spin },
{ "NDIS thread lock", &lock_class_mtx_spin },
#endif
{ "tw_osl_io_lock", &lock_class_mtx_spin },
{ "tw_osl_q_lock", &lock_class_mtx_spin },
{ "tw_cl_io_lock", &lock_class_mtx_spin },
{ "tw_cl_intr_lock", &lock_class_mtx_spin },
{ "tw_cl_gen_lock", &lock_class_mtx_spin },
#ifdef HWPMC_HOOKS
{ "pmc-leaf", &lock_class_mtx_spin },
#endif
{ "blocked lock", &lock_class_mtx_spin },
{ NULL, NULL },
{ NULL, NULL }
};
/*
* Pairs of locks which have been blessed. Witness does not complain about
* order problems with blessed lock pairs. Please do not add an entry to the
* table without an explanatory comment.
*/
static struct witness_blessed blessed_list[] = {
/*
* See the comment in ufs_dirhash.c. Basically, a vnode lock serializes
* both lock orders, so a deadlock cannot happen as a result of this
* LOR.
*/
{ "dirhash", "bufwait" },
/*
* A UFS vnode may be locked in vget() while a buffer belonging to the
* parent directory vnode is locked.
*/
{ "ufs", "bufwait" },
};
/*
* This global is set to 0 once it becomes safe to use the witness code.
*/
static int witness_cold = 1;
/*
* This global is set to 1 once the static lock orders have been enrolled
* so that a warning can be issued for any spin locks enrolled later.
*/
static int witness_spin_warn = 0;
/* Trim useless garbage from filenames. */
static const char *
fixup_filename(const char *file)
{
if (file == NULL)
return (NULL);
while (strncmp(file, "../", 3) == 0)
file += 3;
return (file);
}
/*
* Calculate the size of early witness structures.
*/
int
witness_startup_count(void)
{
int sz;
sz = sizeof(struct witness) * witness_count;
sz += sizeof(*w_rmatrix) * (witness_count + 1);
sz += sizeof(*w_rmatrix[0]) * (witness_count + 1) *
(witness_count + 1);
return (sz);
}
/*
* The WITNESS-enabled diagnostic code. Note that the witness code does
* assume that the early boot is single-threaded at least until after this
* routine is completed.
*/
void
witness_startup(void *mem)
{
struct lock_object *lock;
struct witness_order_list_entry *order;
struct witness *w, *w1;
uintptr_t p;
int i;
p = (uintptr_t)mem;
w_data = (void *)p;
p += sizeof(struct witness) * witness_count;
w_rmatrix = (void *)p;
p += sizeof(*w_rmatrix) * (witness_count + 1);
for (i = 0; i < witness_count + 1; i++) {
w_rmatrix[i] = (void *)p;
p += sizeof(*w_rmatrix[i]) * (witness_count + 1);
}
badstack_sbuf_size = witness_count * 256;
/*
* We have to release Giant before initializing its witness
* structure so that WITNESS doesn't get confused.
*/
mtx_unlock(&Giant);
mtx_assert(&Giant, MA_NOTOWNED);
CTR1(KTR_WITNESS, "%s: initializing witness", __func__);
mtx_init(&w_mtx, "witness lock", NULL, MTX_SPIN | MTX_QUIET |
MTX_NOWITNESS | MTX_NOPROFILE);
for (i = witness_count - 1; i >= 0; i--) {
w = &w_data[i];
memset(w, 0, sizeof(*w));
w_data[i].w_index = i; /* Witness index never changes. */
witness_free(w);
}
KASSERT(STAILQ_FIRST(&w_free)->w_index == 0,
("%s: Invalid list of free witness objects", __func__));
/* Witness with index 0 is not used to aid in debugging. */
STAILQ_REMOVE_HEAD(&w_free, w_list);
w_free_cnt--;
for (i = 0; i < witness_count; i++) {
memset(w_rmatrix[i], 0, sizeof(*w_rmatrix[i]) *
(witness_count + 1));
}
for (i = 0; i < LOCK_CHILDCOUNT; i++)
witness_lock_list_free(&w_locklistdata[i]);
witness_init_hash_tables();
/* First add in all the specified order lists. */
for (order = order_lists; order->w_name != NULL; order++) {
w = enroll(order->w_name, order->w_class);
if (w == NULL)
continue;
w->w_file = "order list";
for (order++; order->w_name != NULL; order++) {
w1 = enroll(order->w_name, order->w_class);
if (w1 == NULL)
continue;
w1->w_file = "order list";
itismychild(w, w1);
w = w1;
}
}
witness_spin_warn = 1;
/* Iterate through all locks and add them to witness. */
for (i = 0; pending_locks[i].wh_lock != NULL; i++) {
lock = pending_locks[i].wh_lock;
KASSERT(lock->lo_flags & LO_WITNESS,
("%s: lock %s is on pending list but not LO_WITNESS",
__func__, lock->lo_name));
lock->lo_witness = enroll(pending_locks[i].wh_type,
LOCK_CLASS(lock));
}
/* Mark the witness code as being ready for use. */
witness_cold = 0;
mtx_lock(&Giant);
}
void
witness_init(struct lock_object *lock, const char *type)
{
struct lock_class *class;
/* Various sanity checks. */
class = LOCK_CLASS(lock);
if ((lock->lo_flags & LO_RECURSABLE) != 0 &&
(class->lc_flags & LC_RECURSABLE) == 0)
kassert_panic("%s: lock (%s) %s can not be recursable",
__func__, class->lc_name, lock->lo_name);
if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
(class->lc_flags & LC_SLEEPABLE) == 0)
kassert_panic("%s: lock (%s) %s can not be sleepable",
__func__, class->lc_name, lock->lo_name);
if ((lock->lo_flags & LO_UPGRADABLE) != 0 &&
(class->lc_flags & LC_UPGRADABLE) == 0)
kassert_panic("%s: lock (%s) %s can not be upgradable",
__func__, class->lc_name, lock->lo_name);
/*
* If we shouldn't watch this lock, then just clear lo_witness.
* Otherwise, if witness_cold is set, then it is too early to
* enroll this lock, so defer it to witness_initialize() by adding
* it to the pending_locks list. If it is not too early, then enroll
* the lock now.
*/
if (witness_watch < 1 || KERNEL_PANICKED() ||
(lock->lo_flags & LO_WITNESS) == 0)
lock->lo_witness = NULL;
else if (witness_cold) {
pending_locks[pending_cnt].wh_lock = lock;
pending_locks[pending_cnt++].wh_type = type;
if (pending_cnt > WITNESS_PENDLIST)
panic("%s: pending locks list is too small, "
"increase WITNESS_PENDLIST\n",
__func__);
} else
lock->lo_witness = enroll(type, class);
}
void
witness_destroy(struct lock_object *lock)
{
struct lock_class *class;
struct witness *w;
class = LOCK_CLASS(lock);
if (witness_cold)
panic("lock (%s) %s destroyed while witness_cold",
class->lc_name, lock->lo_name);
/* XXX: need to verify that no one holds the lock */
if ((lock->lo_flags & LO_WITNESS) == 0 || lock->lo_witness == NULL)
return;
w = lock->lo_witness;
mtx_lock_spin(&w_mtx);
MPASS(w->w_refcount > 0);
w->w_refcount--;
if (w->w_refcount == 0)
depart(w);
mtx_unlock_spin(&w_mtx);
}
#ifdef DDB
static void
witness_ddb_compute_levels(void)
{
struct witness *w;
/*
* First clear all levels.
*/
STAILQ_FOREACH(w, &w_all, w_list)
w->w_ddb_level = -1;
/*
* Look for locks with no parents and level all their descendants.
*/
STAILQ_FOREACH(w, &w_all, w_list) {
/* If the witness has ancestors (is not a root), skip it. */
if (w->w_num_ancestors > 0)
continue;
witness_ddb_level_descendants(w, 0);
}
}
static void
witness_ddb_level_descendants(struct witness *w, int l)
{
int i;
if (w->w_ddb_level >= l)
return;
w->w_ddb_level = l;
l++;
for (i = 1; i <= w_max_used_index; i++) {
if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
witness_ddb_level_descendants(&w_data[i], l);
}
}
static void
witness_ddb_display_descendants(int(*prnt)(const char *fmt, ...),
struct witness *w, int indent)
{
int i;
for (i = 0; i < indent; i++)
prnt(" ");
prnt("%s (type: %s, depth: %d, active refs: %d)",
w->w_name, w->w_class->lc_name,
w->w_ddb_level, w->w_refcount);
if (w->w_displayed) {
prnt(" -- (already displayed)\n");
return;
}
w->w_displayed = 1;
if (w->w_file != NULL && w->w_line != 0)
prnt(" -- last acquired @ %s:%d\n", fixup_filename(w->w_file),
w->w_line);
else
prnt(" -- never acquired\n");
indent++;
WITNESS_INDEX_ASSERT(w->w_index);
for (i = 1; i <= w_max_used_index; i++) {
if (db_pager_quit)
return;
if (w_rmatrix[w->w_index][i] & WITNESS_PARENT)
witness_ddb_display_descendants(prnt, &w_data[i],
indent);
}
}
static void
witness_ddb_display_list(int(*prnt)(const char *fmt, ...),
struct witness_list *list)
{
struct witness *w;
STAILQ_FOREACH(w, list, w_typelist) {
if (w->w_file == NULL || w->w_ddb_level > 0)
continue;
/* This lock has no anscestors - display its descendants. */
witness_ddb_display_descendants(prnt, w, 0);
if (db_pager_quit)
return;
}
}
static void
witness_ddb_display(int(*prnt)(const char *fmt, ...))
{
struct witness *w;
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
witness_ddb_compute_levels();
/* Clear all the displayed flags. */
STAILQ_FOREACH(w, &w_all, w_list)
w->w_displayed = 0;
/*
* First, handle sleep locks which have been acquired at least
* once.
*/
prnt("Sleep locks:\n");
witness_ddb_display_list(prnt, &w_sleep);
if (db_pager_quit)
return;
/*
* Now do spin locks which have been acquired at least once.
*/
prnt("\nSpin locks:\n");
witness_ddb_display_list(prnt, &w_spin);
if (db_pager_quit)
return;
/*
* Finally, any locks which have not been acquired yet.
*/
prnt("\nLocks which were never acquired:\n");
STAILQ_FOREACH(w, &w_all, w_list) {
if (w->w_file != NULL || w->w_refcount == 0)
continue;
prnt("%s (type: %s, depth: %d)\n", w->w_name,
w->w_class->lc_name, w->w_ddb_level);
if (db_pager_quit)
return;
}
}
#endif /* DDB */
int
witness_defineorder(struct lock_object *lock1, struct lock_object *lock2)
{
if (witness_watch == -1 || KERNEL_PANICKED())
return (0);
/* Require locks that witness knows about. */
if (lock1 == NULL || lock1->lo_witness == NULL || lock2 == NULL ||
lock2->lo_witness == NULL)
return (EINVAL);
mtx_assert(&w_mtx, MA_NOTOWNED);
mtx_lock_spin(&w_mtx);
/*
* If we already have either an explicit or implied lock order that
* is the other way around, then return an error.
*/
if (witness_watch &&
isitmydescendant(lock2->lo_witness, lock1->lo_witness)) {
mtx_unlock_spin(&w_mtx);
return (EDOOFUS);
}
/* Try to add the new order. */
CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
lock2->lo_witness->w_name, lock1->lo_witness->w_name);
itismychild(lock1->lo_witness, lock2->lo_witness);
mtx_unlock_spin(&w_mtx);
return (0);
}
void
witness_checkorder(struct lock_object *lock, int flags, const char *file,
int line, struct lock_object *interlock)
{
struct lock_list_entry *lock_list, *lle;
struct lock_instance *lock1, *lock2, *plock;
struct lock_class *class, *iclass;
struct witness *w, *w1;
struct thread *td;
int i, j;
if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL ||
KERNEL_PANICKED())
return;
w = lock->lo_witness;
class = LOCK_CLASS(lock);
td = curthread;
if (class->lc_flags & LC_SLEEPLOCK) {
/*
* Since spin locks include a critical section, this check
* implicitly enforces a lock order of all sleep locks before
* all spin locks.
*/
if (td->td_critnest != 0 && !kdb_active)
kassert_panic("acquiring blockable sleep lock with "
"spinlock or critical section held (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
/*
* If this is the first lock acquired then just return as
* no order checking is needed.
*/
lock_list = td->td_sleeplocks;
if (lock_list == NULL || lock_list->ll_count == 0)
return;
} else {
/*
* If this is the first lock, just return as no order
* checking is needed. Avoid problems with thread
* migration pinning the thread while checking if
* spinlocks are held. If at least one spinlock is held
* the thread is in a safe path and it is allowed to
* unpin it.
*/
sched_pin();
lock_list = PCPU_GET(spinlocks);
if (lock_list == NULL || lock_list->ll_count == 0) {
sched_unpin();
return;
}
sched_unpin();
}
/*
* Check to see if we are recursing on a lock we already own. If
* so, make sure that we don't mismatch exclusive and shared lock
* acquires.
*/
lock1 = find_instance(lock_list, lock);
if (lock1 != NULL) {
if ((lock1->li_flags & LI_EXCLUSIVE) != 0 &&
(flags & LOP_EXCLUSIVE) == 0) {
witness_output("shared lock of (%s) %s @ %s:%d\n",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
witness_output("while exclusively locked from %s:%d\n",
fixup_filename(lock1->li_file), lock1->li_line);
kassert_panic("excl->share");
}
if ((lock1->li_flags & LI_EXCLUSIVE) == 0 &&
(flags & LOP_EXCLUSIVE) != 0) {
witness_output("exclusive lock of (%s) %s @ %s:%d\n",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
witness_output("while share locked from %s:%d\n",
fixup_filename(lock1->li_file), lock1->li_line);
kassert_panic("share->excl");
}
return;
}
/* Warn if the interlock is not locked exactly once. */
if (interlock != NULL) {
iclass = LOCK_CLASS(interlock);
lock1 = find_instance(lock_list, interlock);
if (lock1 == NULL)
kassert_panic("interlock (%s) %s not locked @ %s:%d",
iclass->lc_name, interlock->lo_name,
fixup_filename(file), line);
else if ((lock1->li_flags & LI_RECURSEMASK) != 0)
kassert_panic("interlock (%s) %s recursed @ %s:%d",
iclass->lc_name, interlock->lo_name,
fixup_filename(file), line);
}
/*
* Find the previously acquired lock, but ignore interlocks.
*/
plock = &lock_list->ll_children[lock_list->ll_count - 1];
if (interlock != NULL && plock->li_lock == interlock) {
if (lock_list->ll_count > 1)
plock =
&lock_list->ll_children[lock_list->ll_count - 2];
else {
lle = lock_list->ll_next;
/*
* The interlock is the only lock we hold, so
* simply return.
*/
if (lle == NULL)
return;
plock = &lle->ll_children[lle->ll_count - 1];
}
}
/*
* Try to perform most checks without a lock. If this succeeds we
* can skip acquiring the lock and return success. Otherwise we redo
* the check with the lock held to handle races with concurrent updates.
*/
w1 = plock->li_lock->lo_witness;
if (witness_lock_order_check(w1, w))
return;
mtx_lock_spin(&w_mtx);
if (witness_lock_order_check(w1, w)) {
mtx_unlock_spin(&w_mtx);
return;
}
witness_lock_order_add(w1, w);
/*
* Check for duplicate locks of the same type. Note that we only
* have to check for this on the last lock we just acquired. Any
* other cases will be caught as lock order violations.
*/
if (w1 == w) {
i = w->w_index;
if (!(lock->lo_flags & LO_DUPOK) && !(flags & LOP_DUPOK) &&
!(w_rmatrix[i][i] & WITNESS_REVERSAL)) {
w_rmatrix[i][i] |= WITNESS_REVERSAL;
w->w_reversed = 1;
mtx_unlock_spin(&w_mtx);
witness_output(
"acquiring duplicate lock of same type: \"%s\"\n",
w->w_name);
witness_output(" 1st %s @ %s:%d\n", plock->li_lock->lo_name,
fixup_filename(plock->li_file), plock->li_line);
witness_output(" 2nd %s @ %s:%d\n", lock->lo_name,
fixup_filename(file), line);
witness_debugger(1, __func__);
} else
mtx_unlock_spin(&w_mtx);
return;
}
mtx_assert(&w_mtx, MA_OWNED);
/*
* If we know that the lock we are acquiring comes after
* the lock we most recently acquired in the lock order tree,
* then there is no need for any further checks.
*/
if (isitmychild(w1, w))
goto out;
for (j = 0, lle = lock_list; lle != NULL; lle = lle->ll_next) {
for (i = lle->ll_count - 1; i >= 0; i--, j++) {
MPASS(j < LOCK_CHILDCOUNT * LOCK_NCHILDREN);
lock1 = &lle->ll_children[i];
/*
* Ignore the interlock.
*/
if (interlock == lock1->li_lock)
continue;
/*
* If this lock doesn't undergo witness checking,
* then skip it.
*/
w1 = lock1->li_lock->lo_witness;
if (w1 == NULL) {
KASSERT((lock1->li_lock->lo_flags & LO_WITNESS) == 0,
("lock missing witness structure"));
continue;
}
/*
* If we are locking Giant and this is a sleepable
* lock, then skip it.
*/
if ((lock1->li_flags & LI_SLEEPABLE) != 0 &&
lock == &Giant.lock_object)
continue;
/*
* If we are locking a sleepable lock and this lock
* is Giant, then skip it.
*/
if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
(flags & LOP_NOSLEEP) == 0 &&
lock1->li_lock == &Giant.lock_object)
continue;
/*
* If we are locking a sleepable lock and this lock
* isn't sleepable, we want to treat it as a lock
* order violation to enfore a general lock order of
* sleepable locks before non-sleepable locks.
*/
if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
(flags & LOP_NOSLEEP) == 0 &&
(lock1->li_flags & LI_SLEEPABLE) == 0)
goto reversal;
/*
* If we are locking Giant and this is a non-sleepable
* lock, then treat it as a reversal.
*/
if ((lock1->li_flags & LI_SLEEPABLE) == 0 &&
lock == &Giant.lock_object)
goto reversal;
/*
* Check the lock order hierarchy for a reveresal.
*/
if (!isitmydescendant(w, w1))
continue;
reversal:
/*
* We have a lock order violation, check to see if it
* is allowed or has already been yelled about.
*/
/* Bail if this violation is known */
if (w_rmatrix[w1->w_index][w->w_index] & WITNESS_REVERSAL)
goto out;
/* Record this as a violation */
w_rmatrix[w1->w_index][w->w_index] |= WITNESS_REVERSAL;
w_rmatrix[w->w_index][w1->w_index] |= WITNESS_REVERSAL;
w->w_reversed = w1->w_reversed = 1;
witness_increment_graph_generation();
/*
* If the lock order is blessed, bail before logging
* anything. We don't look for other lock order
* violations though, which may be a bug.
*/
if (blessed(w, w1))
goto out;
mtx_unlock_spin(&w_mtx);
#ifdef WITNESS_NO_VNODE
/*
* There are known LORs between VNODE locks. They are
* not an indication of a bug. VNODE locks are flagged
* as such (LO_IS_VNODE) and we don't yell if the LOR
* is between 2 VNODE locks.
*/
if ((lock->lo_flags & LO_IS_VNODE) != 0 &&
(lock1->li_lock->lo_flags & LO_IS_VNODE) != 0)
return;
#endif
/*
* Ok, yell about it.
*/
if ((lock->lo_flags & LO_SLEEPABLE) != 0 &&
(flags & LOP_NOSLEEP) == 0 &&
(lock1->li_flags & LI_SLEEPABLE) == 0)
witness_output(
"lock order reversal: (sleepable after non-sleepable)\n");
else if ((lock1->li_flags & LI_SLEEPABLE) == 0
&& lock == &Giant.lock_object)
witness_output(
"lock order reversal: (Giant after non-sleepable)\n");
else
witness_output("lock order reversal:\n");
/*
* Try to locate an earlier lock with
* witness w in our list.
*/
do {
lock2 = &lle->ll_children[i];
MPASS(lock2->li_lock != NULL);
if (lock2->li_lock->lo_witness == w)
break;
if (i == 0 && lle->ll_next != NULL) {
lle = lle->ll_next;
i = lle->ll_count - 1;
MPASS(i >= 0 && i < LOCK_NCHILDREN);
} else
i--;
} while (i >= 0);
if (i < 0) {
witness_output(" 1st %p %s (%s) @ %s:%d\n",
lock1->li_lock, lock1->li_lock->lo_name,
w1->w_name, fixup_filename(lock1->li_file),
lock1->li_line);
witness_output(" 2nd %p %s (%s) @ %s:%d\n", lock,
lock->lo_name, w->w_name,
fixup_filename(file), line);
} else {
witness_output(" 1st %p %s (%s) @ %s:%d\n",
lock2->li_lock, lock2->li_lock->lo_name,
lock2->li_lock->lo_witness->w_name,
fixup_filename(lock2->li_file),
lock2->li_line);
witness_output(" 2nd %p %s (%s) @ %s:%d\n",
lock1->li_lock, lock1->li_lock->lo_name,
w1->w_name, fixup_filename(lock1->li_file),
lock1->li_line);
witness_output(" 3rd %p %s (%s) @ %s:%d\n", lock,
lock->lo_name, w->w_name,
fixup_filename(file), line);
}
witness_debugger(1, __func__);
return;
}
}
/*
* If requested, build a new lock order. However, don't build a new
* relationship between a sleepable lock and Giant if it is in the
* wrong direction. The correct lock order is that sleepable locks
* always come before Giant.
*/
if (flags & LOP_NEWORDER &&
!(plock->li_lock == &Giant.lock_object &&
(lock->lo_flags & LO_SLEEPABLE) != 0 &&
(flags & LOP_NOSLEEP) == 0)) {
CTR3(KTR_WITNESS, "%s: adding %s as a child of %s", __func__,
w->w_name, plock->li_lock->lo_witness->w_name);
itismychild(plock->li_lock->lo_witness, w);
}
out:
mtx_unlock_spin(&w_mtx);
}
void
witness_lock(struct lock_object *lock, int flags, const char *file, int line)
{
struct lock_list_entry **lock_list, *lle;
struct lock_instance *instance;
struct witness *w;
struct thread *td;
if (witness_cold || witness_watch == -1 || lock->lo_witness == NULL ||
KERNEL_PANICKED())
return;
w = lock->lo_witness;
td = curthread;
/* Determine lock list for this lock. */
if (LOCK_CLASS(lock)->lc_flags & LC_SLEEPLOCK)
lock_list = &td->td_sleeplocks;
else
lock_list = PCPU_PTR(spinlocks);
/* Check to see if we are recursing on a lock we already own. */
instance = find_instance(*lock_list, lock);
if (instance != NULL) {
instance->li_flags++;
CTR4(KTR_WITNESS, "%s: pid %d recursed on %s r=%d", __func__,
td->td_proc->p_pid, lock->lo_name,
instance->li_flags & LI_RECURSEMASK);
instance->li_file = file;
instance->li_line = line;
return;
}
/* Update per-witness last file and line acquire. */
w->w_file = file;
w->w_line = line;
/* Find the next open lock instance in the list and fill it. */
lle = *lock_list;
if (lle == NULL || lle->ll_count == LOCK_NCHILDREN) {
lle = witness_lock_list_get();
if (lle == NULL)
return;
lle->ll_next = *lock_list;
CTR3(KTR_WITNESS, "%s: pid %d added lle %p", __func__,
td->td_proc->p_pid, lle);
*lock_list = lle;
}
instance = &lle->ll_children[lle->ll_count++];
instance->li_lock = lock;
instance->li_line = line;
instance->li_file = file;
instance->li_flags = 0;
if ((flags & LOP_EXCLUSIVE) != 0)
instance->li_flags |= LI_EXCLUSIVE;
if ((lock->lo_flags & LO_SLEEPABLE) != 0 && (flags & LOP_NOSLEEP) == 0)
instance->li_flags |= LI_SLEEPABLE;
CTR4(KTR_WITNESS, "%s: pid %d added %s as lle[%d]", __func__,
td->td_proc->p_pid, lock->lo_name, lle->ll_count - 1);
}
void
witness_upgrade(struct lock_object *lock, int flags, const char *file, int line)
{
struct lock_instance *instance;
struct lock_class *class;
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
if (lock->lo_witness == NULL || witness_watch == -1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if (witness_watch) {
if ((lock->lo_flags & LO_UPGRADABLE) == 0)
kassert_panic(
"upgrade of non-upgradable lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((class->lc_flags & LC_SLEEPLOCK) == 0)
kassert_panic(
"upgrade of non-sleep lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
}
instance = find_instance(curthread->td_sleeplocks, lock);
if (instance == NULL) {
kassert_panic("upgrade of unlocked lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
return;
}
if (witness_watch) {
if ((instance->li_flags & LI_EXCLUSIVE) != 0)
kassert_panic(
"upgrade of exclusive lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((instance->li_flags & LI_RECURSEMASK) != 0)
kassert_panic(
"upgrade of recursed lock (%s) %s r=%d @ %s:%d",
class->lc_name, lock->lo_name,
instance->li_flags & LI_RECURSEMASK,
fixup_filename(file), line);
}
instance->li_flags |= LI_EXCLUSIVE;
}
void
witness_downgrade(struct lock_object *lock, int flags, const char *file,
int line)
{
struct lock_instance *instance;
struct lock_class *class;
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
if (lock->lo_witness == NULL || witness_watch == -1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if (witness_watch) {
if ((lock->lo_flags & LO_UPGRADABLE) == 0)
kassert_panic(
"downgrade of non-upgradable lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((class->lc_flags & LC_SLEEPLOCK) == 0)
kassert_panic(
"downgrade of non-sleep lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
}
instance = find_instance(curthread->td_sleeplocks, lock);
if (instance == NULL) {
kassert_panic("downgrade of unlocked lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
return;
}
if (witness_watch) {
if ((instance->li_flags & LI_EXCLUSIVE) == 0)
kassert_panic(
"downgrade of shared lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((instance->li_flags & LI_RECURSEMASK) != 0)
kassert_panic(
"downgrade of recursed lock (%s) %s r=%d @ %s:%d",
class->lc_name, lock->lo_name,
instance->li_flags & LI_RECURSEMASK,
fixup_filename(file), line);
}
instance->li_flags &= ~LI_EXCLUSIVE;
}
void
witness_unlock(struct lock_object *lock, int flags, const char *file, int line)
{
struct lock_list_entry **lock_list, *lle;
struct lock_instance *instance;
struct lock_class *class;
struct thread *td;
register_t s;
int i, j;
if (witness_cold || lock->lo_witness == NULL || KERNEL_PANICKED())
return;
td = curthread;
class = LOCK_CLASS(lock);
/* Find lock instance associated with this lock. */
if (class->lc_flags & LC_SLEEPLOCK)
lock_list = &td->td_sleeplocks;
else
lock_list = PCPU_PTR(spinlocks);
lle = *lock_list;
for (; *lock_list != NULL; lock_list = &(*lock_list)->ll_next)
for (i = 0; i < (*lock_list)->ll_count; i++) {
instance = &(*lock_list)->ll_children[i];
if (instance->li_lock == lock)
goto found;
}
/*
* When disabling WITNESS through witness_watch we could end up in
* having registered locks in the td_sleeplocks queue.
* We have to make sure we flush these queues, so just search for
* eventual register locks and remove them.
*/
if (witness_watch > 0) {
kassert_panic("lock (%s) %s not locked @ %s:%d", class->lc_name,
lock->lo_name, fixup_filename(file), line);
return;
} else {
return;
}
found:
/* First, check for shared/exclusive mismatches. */
if ((instance->li_flags & LI_EXCLUSIVE) != 0 && witness_watch > 0 &&
(flags & LOP_EXCLUSIVE) == 0) {
witness_output("shared unlock of (%s) %s @ %s:%d\n",
class->lc_name, lock->lo_name, fixup_filename(file), line);
witness_output("while exclusively locked from %s:%d\n",
fixup_filename(instance->li_file), instance->li_line);
kassert_panic("excl->ushare");
}
if ((instance->li_flags & LI_EXCLUSIVE) == 0 && witness_watch > 0 &&
(flags & LOP_EXCLUSIVE) != 0) {
witness_output("exclusive unlock of (%s) %s @ %s:%d\n",
class->lc_name, lock->lo_name, fixup_filename(file), line);
witness_output("while share locked from %s:%d\n",
fixup_filename(instance->li_file),
instance->li_line);
kassert_panic("share->uexcl");
}
/* If we are recursed, unrecurse. */
if ((instance->li_flags & LI_RECURSEMASK) > 0) {
CTR4(KTR_WITNESS, "%s: pid %d unrecursed on %s r=%d", __func__,
td->td_proc->p_pid, instance->li_lock->lo_name,
instance->li_flags);
instance->li_flags--;
return;
}
/* The lock is now being dropped, check for NORELEASE flag */
if ((instance->li_flags & LI_NORELEASE) != 0 && witness_watch > 0) {
witness_output("forbidden unlock of (%s) %s @ %s:%d\n",
class->lc_name, lock->lo_name, fixup_filename(file), line);
kassert_panic("lock marked norelease");
}
/* Otherwise, remove this item from the list. */
s = intr_disable();
CTR4(KTR_WITNESS, "%s: pid %d removed %s from lle[%d]", __func__,
td->td_proc->p_pid, instance->li_lock->lo_name,
(*lock_list)->ll_count - 1);
for (j = i; j < (*lock_list)->ll_count - 1; j++)
(*lock_list)->ll_children[j] =
(*lock_list)->ll_children[j + 1];
(*lock_list)->ll_count--;
intr_restore(s);
/*
* In order to reduce contention on w_mtx, we want to keep always an
* head object into lists so that frequent allocation from the
* free witness pool (and subsequent locking) is avoided.
* In order to maintain the current code simple, when the head
* object is totally unloaded it means also that we do not have
* further objects in the list, so the list ownership needs to be
* hand over to another object if the current head needs to be freed.
*/
if ((*lock_list)->ll_count == 0) {
if (*lock_list == lle) {
if (lle->ll_next == NULL)
return;
} else
lle = *lock_list;
*lock_list = lle->ll_next;
CTR3(KTR_WITNESS, "%s: pid %d removed lle %p", __func__,
td->td_proc->p_pid, lle);
witness_lock_list_free(lle);
}
}
void
witness_thread_exit(struct thread *td)
{
struct lock_list_entry *lle;
int i, n;
lle = td->td_sleeplocks;
if (lle == NULL || KERNEL_PANICKED())
return;
if (lle->ll_count != 0) {
for (n = 0; lle != NULL; lle = lle->ll_next)
for (i = lle->ll_count - 1; i >= 0; i--) {
if (n == 0)
witness_output(
"Thread %p exiting with the following locks held:\n", td);
n++;
witness_list_lock(&lle->ll_children[i],
witness_output);
}
kassert_panic(
"Thread %p cannot exit while holding sleeplocks\n", td);
}
witness_lock_list_free(lle);
}
/*
* Warn if any locks other than 'lock' are held. Flags can be passed in to
* exempt Giant and sleepable locks from the checks as well. If any
* non-exempt locks are held, then a supplied message is printed to the
* output channel along with a list of the offending locks. If indicated in the
* flags then a failure results in a panic as well.
*/
int
witness_warn(int flags, struct lock_object *lock, const char *fmt, ...)
{
struct lock_list_entry *lock_list, *lle;
struct lock_instance *lock1;
struct thread *td;
va_list ap;
int i, n;
if (witness_cold || witness_watch < 1 || KERNEL_PANICKED())
return (0);
n = 0;
td = curthread;
for (lle = td->td_sleeplocks; lle != NULL; lle = lle->ll_next)
for (i = lle->ll_count - 1; i >= 0; i--) {
lock1 = &lle->ll_children[i];
if (lock1->li_lock == lock)
continue;
if (flags & WARN_GIANTOK &&
lock1->li_lock == &Giant.lock_object)
continue;
if (flags & WARN_SLEEPOK &&
(lock1->li_flags & LI_SLEEPABLE) != 0)
continue;
if (n == 0) {
va_start(ap, fmt);
vprintf(fmt, ap);
va_end(ap);
printf(" with the following %slocks held:\n",
(flags & WARN_SLEEPOK) != 0 ?
"non-sleepable " : "");
}
n++;
witness_list_lock(lock1, printf);
}
/*
* Pin the thread in order to avoid problems with thread migration.
* Once that all verifies are passed about spinlocks ownership,
* the thread is in a safe path and it can be unpinned.
*/
sched_pin();
lock_list = PCPU_GET(spinlocks);
if (lock_list != NULL && lock_list->ll_count != 0) {
sched_unpin();
/*
* We should only have one spinlock and as long as
* the flags cannot match for this locks class,
* check if the first spinlock is the one curthread
* should hold.
*/
lock1 = &lock_list->ll_children[lock_list->ll_count - 1];
if (lock_list->ll_count == 1 && lock_list->ll_next == NULL &&
lock1->li_lock == lock && n == 0)
return (0);
va_start(ap, fmt);
vprintf(fmt, ap);
va_end(ap);
printf(" with the following %slocks held:\n",
(flags & WARN_SLEEPOK) != 0 ? "non-sleepable " : "");
n += witness_list_locks(&lock_list, printf);
} else
sched_unpin();
if (flags & WARN_PANIC && n)
kassert_panic("%s", __func__);
else
witness_debugger(n, __func__);
return (n);
}
const char *
witness_file(struct lock_object *lock)
{
struct witness *w;
if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL)
return ("?");
w = lock->lo_witness;
return (w->w_file);
}
int
witness_line(struct lock_object *lock)
{
struct witness *w;
if (witness_cold || witness_watch < 1 || lock->lo_witness == NULL)
return (0);
w = lock->lo_witness;
return (w->w_line);
}
static struct witness *
enroll(const char *description, struct lock_class *lock_class)
{
struct witness *w;
MPASS(description != NULL);
if (witness_watch == -1 || KERNEL_PANICKED())
return (NULL);
if ((lock_class->lc_flags & LC_SPINLOCK)) {
if (witness_skipspin)
return (NULL);
} else if ((lock_class->lc_flags & LC_SLEEPLOCK) == 0) {
kassert_panic("lock class %s is not sleep or spin",
lock_class->lc_name);
return (NULL);
}
mtx_lock_spin(&w_mtx);
w = witness_hash_get(description);
if (w)
goto found;
if ((w = witness_get()) == NULL)
return (NULL);
MPASS(strlen(description) < MAX_W_NAME);
strcpy(w->w_name, description);
w->w_class = lock_class;
w->w_refcount = 1;
STAILQ_INSERT_HEAD(&w_all, w, w_list);
if (lock_class->lc_flags & LC_SPINLOCK) {
STAILQ_INSERT_HEAD(&w_spin, w, w_typelist);
w_spin_cnt++;
} else if (lock_class->lc_flags & LC_SLEEPLOCK) {
STAILQ_INSERT_HEAD(&w_sleep, w, w_typelist);
w_sleep_cnt++;
}
/* Insert new witness into the hash */
witness_hash_put(w);
witness_increment_graph_generation();
mtx_unlock_spin(&w_mtx);
return (w);
found:
w->w_refcount++;
if (w->w_refcount == 1)
w->w_class = lock_class;
mtx_unlock_spin(&w_mtx);
if (lock_class != w->w_class)
kassert_panic(
"lock (%s) %s does not match earlier (%s) lock",
description, lock_class->lc_name,
w->w_class->lc_name);
return (w);
}
static void
depart(struct witness *w)
{
MPASS(w->w_refcount == 0);
if (w->w_class->lc_flags & LC_SLEEPLOCK) {
w_sleep_cnt--;
} else {
w_spin_cnt--;
}
/*
* Set file to NULL as it may point into a loadable module.
*/
w->w_file = NULL;
w->w_line = 0;
witness_increment_graph_generation();
}
static void
adopt(struct witness *parent, struct witness *child)
{
int pi, ci, i, j;
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
/* If the relationship is already known, there's no work to be done. */
if (isitmychild(parent, child))
return;
/* When the structure of the graph changes, bump up the generation. */
witness_increment_graph_generation();
/*
* The hard part ... create the direct relationship, then propagate all
* indirect relationships.
*/
pi = parent->w_index;
ci = child->w_index;
WITNESS_INDEX_ASSERT(pi);
WITNESS_INDEX_ASSERT(ci);
MPASS(pi != ci);
w_rmatrix[pi][ci] |= WITNESS_PARENT;
w_rmatrix[ci][pi] |= WITNESS_CHILD;
/*
* If parent was not already an ancestor of child,
* then we increment the descendant and ancestor counters.
*/
if ((w_rmatrix[pi][ci] & WITNESS_ANCESTOR) == 0) {
parent->w_num_descendants++;
child->w_num_ancestors++;
}
/*
* Find each ancestor of 'pi'. Note that 'pi' itself is counted as
* an ancestor of 'pi' during this loop.
*/
for (i = 1; i <= w_max_used_index; i++) {
if ((w_rmatrix[i][pi] & WITNESS_ANCESTOR_MASK) == 0 &&
(i != pi))
continue;
/* Find each descendant of 'i' and mark it as a descendant. */
for (j = 1; j <= w_max_used_index; j++) {
/*
* Skip children that are already marked as
* descendants of 'i'.
*/
if (w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK)
continue;
/*
* We are only interested in descendants of 'ci'. Note
* that 'ci' itself is counted as a descendant of 'ci'.
*/
if ((w_rmatrix[ci][j] & WITNESS_ANCESTOR_MASK) == 0 &&
(j != ci))
continue;
w_rmatrix[i][j] |= WITNESS_ANCESTOR;
w_rmatrix[j][i] |= WITNESS_DESCENDANT;
w_data[i].w_num_descendants++;
w_data[j].w_num_ancestors++;
/*
* Make sure we aren't marking a node as both an
* ancestor and descendant. We should have caught
* this as a lock order reversal earlier.
*/
if ((w_rmatrix[i][j] & WITNESS_ANCESTOR_MASK) &&
(w_rmatrix[i][j] & WITNESS_DESCENDANT_MASK)) {
printf("witness rmatrix paradox! [%d][%d]=%d "
"both ancestor and descendant\n",
i, j, w_rmatrix[i][j]);
kdb_backtrace();
printf("Witness disabled.\n");
witness_watch = -1;
}
if ((w_rmatrix[j][i] & WITNESS_ANCESTOR_MASK) &&
(w_rmatrix[j][i] & WITNESS_DESCENDANT_MASK)) {
printf("witness rmatrix paradox! [%d][%d]=%d "
"both ancestor and descendant\n",
j, i, w_rmatrix[j][i]);
kdb_backtrace();
printf("Witness disabled.\n");
witness_watch = -1;
}
}
}
}
static void
itismychild(struct witness *parent, struct witness *child)
{
int unlocked;
MPASS(child != NULL && parent != NULL);
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
if (!witness_lock_type_equal(parent, child)) {
if (witness_cold == 0) {
unlocked = 1;
mtx_unlock_spin(&w_mtx);
} else {
unlocked = 0;
}
kassert_panic(
"%s: parent \"%s\" (%s) and child \"%s\" (%s) are not "
"the same lock type", __func__, parent->w_name,
parent->w_class->lc_name, child->w_name,
child->w_class->lc_name);
if (unlocked)
mtx_lock_spin(&w_mtx);
}
adopt(parent, child);
}
/*
* Generic code for the isitmy*() functions. The rmask parameter is the
* expected relationship of w1 to w2.
*/
static int
_isitmyx(struct witness *w1, struct witness *w2, int rmask, const char *fname)
{
unsigned char r1, r2;
int i1, i2;
i1 = w1->w_index;
i2 = w2->w_index;
WITNESS_INDEX_ASSERT(i1);
WITNESS_INDEX_ASSERT(i2);
r1 = w_rmatrix[i1][i2] & WITNESS_RELATED_MASK;
r2 = w_rmatrix[i2][i1] & WITNESS_RELATED_MASK;
/* The flags on one better be the inverse of the flags on the other */
if (!((WITNESS_ATOD(r1) == r2 && WITNESS_DTOA(r2) == r1) ||
(WITNESS_DTOA(r1) == r2 && WITNESS_ATOD(r2) == r1))) {
/* Don't squawk if we're potentially racing with an update. */
if (!mtx_owned(&w_mtx))
return (0);
printf("%s: rmatrix mismatch between %s (index %d) and %s "
"(index %d): w_rmatrix[%d][%d] == %hhx but "
"w_rmatrix[%d][%d] == %hhx\n",
fname, w1->w_name, i1, w2->w_name, i2, i1, i2, r1,
i2, i1, r2);
kdb_backtrace();
printf("Witness disabled.\n");
witness_watch = -1;
}
return (r1 & rmask);
}
/*
* Checks if @child is a direct child of @parent.
*/
static int
isitmychild(struct witness *parent, struct witness *child)
{
return (_isitmyx(parent, child, WITNESS_PARENT, __func__));
}
/*
* Checks if @descendant is a direct or inderect descendant of @ancestor.
*/
static int
isitmydescendant(struct witness *ancestor, struct witness *descendant)
{
return (_isitmyx(ancestor, descendant, WITNESS_ANCESTOR_MASK,
__func__));
}
static int
blessed(struct witness *w1, struct witness *w2)
{
int i;
struct witness_blessed *b;
for (i = 0; i < nitems(blessed_list); i++) {
b = &blessed_list[i];
if (strcmp(w1->w_name, b->b_lock1) == 0) {
if (strcmp(w2->w_name, b->b_lock2) == 0)
return (1);
continue;
}
if (strcmp(w1->w_name, b->b_lock2) == 0)
if (strcmp(w2->w_name, b->b_lock1) == 0)
return (1);
}
return (0);
}
static struct witness *
witness_get(void)
{
struct witness *w;
int index;
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
if (witness_watch == -1) {
mtx_unlock_spin(&w_mtx);
return (NULL);
}
if (STAILQ_EMPTY(&w_free)) {
witness_watch = -1;
mtx_unlock_spin(&w_mtx);
printf("WITNESS: unable to allocate a new witness object\n");
return (NULL);
}
w = STAILQ_FIRST(&w_free);
STAILQ_REMOVE_HEAD(&w_free, w_list);
w_free_cnt--;
index = w->w_index;
MPASS(index > 0 && index == w_max_used_index+1 &&
index < witness_count);
bzero(w, sizeof(*w));
w->w_index = index;
if (index > w_max_used_index)
w_max_used_index = index;
return (w);
}
static void
witness_free(struct witness *w)
{
STAILQ_INSERT_HEAD(&w_free, w, w_list);
w_free_cnt++;
}
static struct lock_list_entry *
witness_lock_list_get(void)
{
struct lock_list_entry *lle;
if (witness_watch == -1)
return (NULL);
mtx_lock_spin(&w_mtx);
lle = w_lock_list_free;
if (lle == NULL) {
witness_watch = -1;
mtx_unlock_spin(&w_mtx);
printf("%s: witness exhausted\n", __func__);
return (NULL);
}
w_lock_list_free = lle->ll_next;
mtx_unlock_spin(&w_mtx);
bzero(lle, sizeof(*lle));
return (lle);
}
static void
witness_lock_list_free(struct lock_list_entry *lle)
{
mtx_lock_spin(&w_mtx);
lle->ll_next = w_lock_list_free;
w_lock_list_free = lle;
mtx_unlock_spin(&w_mtx);
}
static struct lock_instance *
find_instance(struct lock_list_entry *list, const struct lock_object *lock)
{
struct lock_list_entry *lle;
struct lock_instance *instance;
int i;
for (lle = list; lle != NULL; lle = lle->ll_next)
for (i = lle->ll_count - 1; i >= 0; i--) {
instance = &lle->ll_children[i];
if (instance->li_lock == lock)
return (instance);
}
return (NULL);
}
static void
witness_list_lock(struct lock_instance *instance,
int (*prnt)(const char *fmt, ...))
{
struct lock_object *lock;
lock = instance->li_lock;
prnt("%s %s %s", (instance->li_flags & LI_EXCLUSIVE) != 0 ?
"exclusive" : "shared", LOCK_CLASS(lock)->lc_name, lock->lo_name);
if (lock->lo_witness->w_name != lock->lo_name)
prnt(" (%s)", lock->lo_witness->w_name);
prnt(" r = %d (%p) locked @ %s:%d\n",
instance->li_flags & LI_RECURSEMASK, lock,
fixup_filename(instance->li_file), instance->li_line);
}
static int
witness_output(const char *fmt, ...)
{
va_list ap;
int ret;
va_start(ap, fmt);
ret = witness_voutput(fmt, ap);
va_end(ap);
return (ret);
}
static int
witness_voutput(const char *fmt, va_list ap)
{
int ret;
ret = 0;
switch (witness_channel) {
case WITNESS_CONSOLE:
ret = vprintf(fmt, ap);
break;
case WITNESS_LOG:
vlog(LOG_NOTICE, fmt, ap);
break;
case WITNESS_NONE:
break;
}
return (ret);
}
#ifdef DDB
static int
witness_thread_has_locks(struct thread *td)
{
if (td->td_sleeplocks == NULL)
return (0);
return (td->td_sleeplocks->ll_count != 0);
}
static int
witness_proc_has_locks(struct proc *p)
{
struct thread *td;
FOREACH_THREAD_IN_PROC(p, td) {
if (witness_thread_has_locks(td))
return (1);
}
return (0);
}
#endif
int
witness_list_locks(struct lock_list_entry **lock_list,
int (*prnt)(const char *fmt, ...))
{
struct lock_list_entry *lle;
int i, nheld;
nheld = 0;
for (lle = *lock_list; lle != NULL; lle = lle->ll_next)
for (i = lle->ll_count - 1; i >= 0; i--) {
witness_list_lock(&lle->ll_children[i], prnt);
nheld++;
}
return (nheld);
}
/*
* This is a bit risky at best. We call this function when we have timed
* out acquiring a spin lock, and we assume that the other CPU is stuck
* with this lock held. So, we go groveling around in the other CPU's
* per-cpu data to try to find the lock instance for this spin lock to
* see when it was last acquired.
*/
void
witness_display_spinlock(struct lock_object *lock, struct thread *owner,
int (*prnt)(const char *fmt, ...))
{
struct lock_instance *instance;
struct pcpu *pc;
if (owner->td_critnest == 0 || owner->td_oncpu == NOCPU)
return;
pc = pcpu_find(owner->td_oncpu);
instance = find_instance(pc->pc_spinlocks, lock);
if (instance != NULL)
witness_list_lock(instance, prnt);
}
void
witness_save(struct lock_object *lock, const char **filep, int *linep)
{
struct lock_list_entry *lock_list;
struct lock_instance *instance;
struct lock_class *class;
/*
* This function is used independently in locking code to deal with
* Giant, SCHEDULER_STOPPED() check can be removed here after Giant
* is gone.
*/
if (SCHEDULER_STOPPED())
return;
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
if (lock->lo_witness == NULL || witness_watch == -1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if (class->lc_flags & LC_SLEEPLOCK)
lock_list = curthread->td_sleeplocks;
else {
if (witness_skipspin)
return;
lock_list = PCPU_GET(spinlocks);
}
instance = find_instance(lock_list, lock);
if (instance == NULL) {
kassert_panic("%s: lock (%s) %s not locked", __func__,
class->lc_name, lock->lo_name);
return;
}
*filep = instance->li_file;
*linep = instance->li_line;
}
void
witness_restore(struct lock_object *lock, const char *file, int line)
{
struct lock_list_entry *lock_list;
struct lock_instance *instance;
struct lock_class *class;
/*
* This function is used independently in locking code to deal with
* Giant, SCHEDULER_STOPPED() check can be removed here after Giant
* is gone.
*/
if (SCHEDULER_STOPPED())
return;
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
if (lock->lo_witness == NULL || witness_watch == -1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if (class->lc_flags & LC_SLEEPLOCK)
lock_list = curthread->td_sleeplocks;
else {
if (witness_skipspin)
return;
lock_list = PCPU_GET(spinlocks);
}
instance = find_instance(lock_list, lock);
if (instance == NULL)
kassert_panic("%s: lock (%s) %s not locked", __func__,
class->lc_name, lock->lo_name);
lock->lo_witness->w_file = file;
lock->lo_witness->w_line = line;
if (instance == NULL)
return;
instance->li_file = file;
instance->li_line = line;
}
void
witness_assert(const struct lock_object *lock, int flags, const char *file,
int line)
{
#ifdef INVARIANT_SUPPORT
struct lock_instance *instance;
struct lock_class *class;
if (lock->lo_witness == NULL || witness_watch < 1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if ((class->lc_flags & LC_SLEEPLOCK) != 0)
instance = find_instance(curthread->td_sleeplocks, lock);
else if ((class->lc_flags & LC_SPINLOCK) != 0)
instance = find_instance(PCPU_GET(spinlocks), lock);
else {
kassert_panic("Lock (%s) %s is not sleep or spin!",
class->lc_name, lock->lo_name);
return;
}
switch (flags) {
case LA_UNLOCKED:
if (instance != NULL)
kassert_panic("Lock (%s) %s locked @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
break;
case LA_LOCKED:
case LA_LOCKED | LA_RECURSED:
case LA_LOCKED | LA_NOTRECURSED:
case LA_SLOCKED:
case LA_SLOCKED | LA_RECURSED:
case LA_SLOCKED | LA_NOTRECURSED:
case LA_XLOCKED:
case LA_XLOCKED | LA_RECURSED:
case LA_XLOCKED | LA_NOTRECURSED:
if (instance == NULL) {
kassert_panic("Lock (%s) %s not locked @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
break;
}
if ((flags & LA_XLOCKED) != 0 &&
(instance->li_flags & LI_EXCLUSIVE) == 0)
kassert_panic(
"Lock (%s) %s not exclusively locked @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((flags & LA_SLOCKED) != 0 &&
(instance->li_flags & LI_EXCLUSIVE) != 0)
kassert_panic(
"Lock (%s) %s exclusively locked @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((flags & LA_RECURSED) != 0 &&
(instance->li_flags & LI_RECURSEMASK) == 0)
kassert_panic("Lock (%s) %s not recursed @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
if ((flags & LA_NOTRECURSED) != 0 &&
(instance->li_flags & LI_RECURSEMASK) != 0)
kassert_panic("Lock (%s) %s recursed @ %s:%d.",
class->lc_name, lock->lo_name,
fixup_filename(file), line);
break;
default:
kassert_panic("Invalid lock assertion at %s:%d.",
fixup_filename(file), line);
}
#endif /* INVARIANT_SUPPORT */
}
static void
witness_setflag(struct lock_object *lock, int flag, int set)
{
struct lock_list_entry *lock_list;
struct lock_instance *instance;
struct lock_class *class;
if (lock->lo_witness == NULL || witness_watch == -1 || KERNEL_PANICKED())
return;
class = LOCK_CLASS(lock);
if (class->lc_flags & LC_SLEEPLOCK)
lock_list = curthread->td_sleeplocks;
else {
if (witness_skipspin)
return;
lock_list = PCPU_GET(spinlocks);
}
instance = find_instance(lock_list, lock);
if (instance == NULL) {
kassert_panic("%s: lock (%s) %s not locked", __func__,
class->lc_name, lock->lo_name);
return;
}
if (set)
instance->li_flags |= flag;
else
instance->li_flags &= ~flag;
}
void
witness_norelease(struct lock_object *lock)
{
witness_setflag(lock, LI_NORELEASE, 1);
}
void
witness_releaseok(struct lock_object *lock)
{
witness_setflag(lock, LI_NORELEASE, 0);
}
#ifdef DDB
static void
witness_ddb_list(struct thread *td)
{
KASSERT(witness_cold == 0, ("%s: witness_cold", __func__));
KASSERT(kdb_active, ("%s: not in the debugger", __func__));
if (witness_watch < 1)
return;
witness_list_locks(&td->td_sleeplocks, db_printf);
/*
* We only handle spinlocks if td == curthread. This is somewhat broken
* if td is currently executing on some other CPU and holds spin locks
* as we won't display those locks. If we had a MI way of getting
* the per-cpu data for a given cpu then we could use
* td->td_oncpu to get the list of spinlocks for this thread
* and "fix" this.
*
* That still wouldn't really fix this unless we locked the scheduler
* lock or stopped the other CPU to make sure it wasn't changing the
* list out from under us. It is probably best to just not try to
* handle threads on other CPU's for now.
*/
if (td == curthread && PCPU_GET(spinlocks) != NULL)
witness_list_locks(PCPU_PTR(spinlocks), db_printf);
}
DB_SHOW_COMMAND(locks, db_witness_list)
{
struct thread *td;
if (have_addr)
td = db_lookup_thread(addr, true);
else
td = kdb_thread;
witness_ddb_list(td);
}
DB_SHOW_ALL_COMMAND(locks, db_witness_list_all)
{
struct thread *td;
struct proc *p;
/*
* It would be nice to list only threads and processes that actually
* held sleep locks, but that information is currently not exported
* by WITNESS.
*/
FOREACH_PROC_IN_SYSTEM(p) {
if (!witness_proc_has_locks(p))
continue;
FOREACH_THREAD_IN_PROC(p, td) {
if (!witness_thread_has_locks(td))
continue;
db_printf("Process %d (%s) thread %p (%d)\n", p->p_pid,
p->p_comm, td, td->td_tid);
witness_ddb_list(td);
if (db_pager_quit)
return;
}
}
}
DB_SHOW_ALIAS(alllocks, db_witness_list_all)
DB_SHOW_COMMAND(witness, db_witness_display)
{
witness_ddb_display(db_printf);
}
#endif
static void
sbuf_print_witness_badstacks(struct sbuf *sb, size_t *oldidx)
{
struct witness_lock_order_data *data1, *data2, *tmp_data1, *tmp_data2;
struct witness *tmp_w1, *tmp_w2, *w1, *w2;
int generation, i, j;
tmp_data1 = NULL;
tmp_data2 = NULL;
tmp_w1 = NULL;
tmp_w2 = NULL;
/* Allocate and init temporary storage space. */
tmp_w1 = malloc(sizeof(struct witness), M_TEMP, M_WAITOK | M_ZERO);
tmp_w2 = malloc(sizeof(struct witness), M_TEMP, M_WAITOK | M_ZERO);
tmp_data1 = malloc(sizeof(struct witness_lock_order_data), M_TEMP,
M_WAITOK | M_ZERO);
tmp_data2 = malloc(sizeof(struct witness_lock_order_data), M_TEMP,
M_WAITOK | M_ZERO);
stack_zero(&tmp_data1->wlod_stack);
stack_zero(&tmp_data2->wlod_stack);
restart:
mtx_lock_spin(&w_mtx);
generation = w_generation;
mtx_unlock_spin(&w_mtx);
sbuf_printf(sb, "Number of known direct relationships is %d\n",
w_lohash.wloh_count);
for (i = 1; i < w_max_used_index; i++) {
mtx_lock_spin(&w_mtx);
if (generation != w_generation) {
mtx_unlock_spin(&w_mtx);
/* The graph has changed, try again. */
*oldidx = 0;
sbuf_clear(sb);
goto restart;
}
w1 = &w_data[i];
if (w1->w_reversed == 0) {
mtx_unlock_spin(&w_mtx);
continue;
}
/* Copy w1 locally so we can release the spin lock. */
*tmp_w1 = *w1;
mtx_unlock_spin(&w_mtx);
if (tmp_w1->w_reversed == 0)
continue;
for (j = 1; j < w_max_used_index; j++) {
if ((w_rmatrix[i][j] & WITNESS_REVERSAL) == 0 || i > j)
continue;
mtx_lock_spin(&w_mtx);
if (generation != w_generation) {
mtx_unlock_spin(&w_mtx);
/* The graph has changed, try again. */
*oldidx = 0;
sbuf_clear(sb);
goto restart;
}
w2 = &w_data[j];
data1 = witness_lock_order_get(w1, w2);
data2 = witness_lock_order_get(w2, w1);
/*
* Copy information locally so we can release the
* spin lock.
*/
*tmp_w2 = *w2;
if (data1) {
stack_zero(&tmp_data1->wlod_stack);
stack_copy(&data1->wlod_stack,
&tmp_data1->wlod_stack);
}
if (data2 && data2 != data1) {
stack_zero(&tmp_data2->wlod_stack);
stack_copy(&data2->wlod_stack,
&tmp_data2->wlod_stack);
}
mtx_unlock_spin(&w_mtx);
if (blessed(tmp_w1, tmp_w2))
continue;
sbuf_printf(sb,
"\nLock order reversal between \"%s\"(%s) and \"%s\"(%s)!\n",
tmp_w1->w_name, tmp_w1->w_class->lc_name,
tmp_w2->w_name, tmp_w2->w_class->lc_name);
if (data1) {
sbuf_printf(sb,
"Lock order \"%s\"(%s) -> \"%s\"(%s) first seen at:\n",
tmp_w1->w_name, tmp_w1->w_class->lc_name,
tmp_w2->w_name, tmp_w2->w_class->lc_name);
stack_sbuf_print(sb, &tmp_data1->wlod_stack);
sbuf_printf(sb, "\n");
}
if (data2 && data2 != data1) {
sbuf_printf(sb,
"Lock order \"%s\"(%s) -> \"%s\"(%s) first seen at:\n",
tmp_w2->w_name, tmp_w2->w_class->lc_name,
tmp_w1->w_name, tmp_w1->w_class->lc_name);
stack_sbuf_print(sb, &tmp_data2->wlod_stack);
sbuf_printf(sb, "\n");
}
}
}
mtx_lock_spin(&w_mtx);
if (generation != w_generation) {
mtx_unlock_spin(&w_mtx);
/*
* The graph changed while we were printing stack data,
* try again.
*/
*oldidx = 0;
sbuf_clear(sb);
goto restart;
}
mtx_unlock_spin(&w_mtx);
/* Free temporary storage space. */
free(tmp_data1, M_TEMP);
free(tmp_data2, M_TEMP);
free(tmp_w1, M_TEMP);
free(tmp_w2, M_TEMP);
}
static int
sysctl_debug_witness_badstacks(SYSCTL_HANDLER_ARGS)
{
struct sbuf *sb;
int error;
if (witness_watch < 1) {
error = SYSCTL_OUT(req, w_notrunning, sizeof(w_notrunning));
return (error);
}
if (witness_cold) {
error = SYSCTL_OUT(req, w_stillcold, sizeof(w_stillcold));
return (error);
}
error = 0;
sb = sbuf_new(NULL, NULL, badstack_sbuf_size, SBUF_AUTOEXTEND);
if (sb == NULL)
return (ENOMEM);
sbuf_print_witness_badstacks(sb, &req->oldidx);
sbuf_finish(sb);
error = SYSCTL_OUT(req, sbuf_data(sb), sbuf_len(sb) + 1);
sbuf_delete(sb);
return (error);
}
#ifdef DDB
static int
sbuf_db_printf_drain(void *arg __unused, const char *data, int len)
{
return (db_printf("%.*s", len, data));
}
DB_SHOW_COMMAND(badstacks, db_witness_badstacks)
{
struct sbuf sb;
char buffer[128];
size_t dummy;
sbuf_new(&sb, buffer, sizeof(buffer), SBUF_FIXEDLEN);
sbuf_set_drain(&sb, sbuf_db_printf_drain, NULL);
sbuf_print_witness_badstacks(&sb, &dummy);
sbuf_finish(&sb);
}
#endif
static int
sysctl_debug_witness_channel(SYSCTL_HANDLER_ARGS)
{
static const struct {
enum witness_channel channel;
const char *name;
} channels[] = {
{ WITNESS_CONSOLE, "console" },
{ WITNESS_LOG, "log" },
{ WITNESS_NONE, "none" },
};
char buf[16];
u_int i;
int error;
buf[0] = '\0';
for (i = 0; i < nitems(channels); i++)
if (witness_channel == channels[i].channel) {
snprintf(buf, sizeof(buf), "%s", channels[i].name);
break;
}
error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
if (error != 0 || req->newptr == NULL)
return (error);
error = EINVAL;
for (i = 0; i < nitems(channels); i++)
if (strcmp(channels[i].name, buf) == 0) {
witness_channel = channels[i].channel;
error = 0;
break;
}
return (error);
}
static int
sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS)
{
struct witness *w;
struct sbuf *sb;
int error;
#ifdef __i386__
error = SYSCTL_OUT(req, w_notallowed, sizeof(w_notallowed));
return (error);
#endif
if (witness_watch < 1) {
error = SYSCTL_OUT(req, w_notrunning, sizeof(w_notrunning));
return (error);
}
if (witness_cold) {
error = SYSCTL_OUT(req, w_stillcold, sizeof(w_stillcold));
return (error);
}
error = 0;
error = sysctl_wire_old_buffer(req, 0);
if (error != 0)
return (error);
sb = sbuf_new_for_sysctl(NULL, NULL, FULLGRAPH_SBUF_SIZE, req);
if (sb == NULL)
return (ENOMEM);
sbuf_printf(sb, "\n");
mtx_lock_spin(&w_mtx);
STAILQ_FOREACH(w, &w_all, w_list)
w->w_displayed = 0;
STAILQ_FOREACH(w, &w_all, w_list)
witness_add_fullgraph(sb, w);
mtx_unlock_spin(&w_mtx);
/*
* Close the sbuf and return to userland.
*/
error = sbuf_finish(sb);
sbuf_delete(sb);
return (error);
}
static int
sysctl_debug_witness_watch(SYSCTL_HANDLER_ARGS)
{
int error, value;
value = witness_watch;
error = sysctl_handle_int(oidp, &value, 0, req);
if (error != 0 || req->newptr == NULL)
return (error);
if (value > 1 || value < -1 ||
(witness_watch == -1 && value != witness_watch))
return (EINVAL);
witness_watch = value;
return (0);
}
static void
witness_add_fullgraph(struct sbuf *sb, struct witness *w)
{
int i;
if (w->w_displayed != 0 || (w->w_file == NULL && w->w_line == 0))
return;
w->w_displayed = 1;
WITNESS_INDEX_ASSERT(w->w_index);
for (i = 1; i <= w_max_used_index; i++) {
if (w_rmatrix[w->w_index][i] & WITNESS_PARENT) {
sbuf_printf(sb, "\"%s\",\"%s\"\n", w->w_name,
w_data[i].w_name);
witness_add_fullgraph(sb, &w_data[i]);
}
}
}
/*
* A simple hash function. Takes a key pointer and a key size. If size == 0,
* interprets the key as a string and reads until the null
* terminator. Otherwise, reads the first size bytes. Returns an unsigned 32-bit
* hash value computed from the key.
*/
static uint32_t
witness_hash_djb2(const uint8_t *key, uint32_t size)
{
unsigned int hash = 5381;
int i;
/* hash = hash * 33 + key[i] */
if (size)
for (i = 0; i < size; i++)
hash = ((hash << 5) + hash) + (unsigned int)key[i];
else
for (i = 0; key[i] != 0; i++)
hash = ((hash << 5) + hash) + (unsigned int)key[i];
return (hash);
}
/*
* Initializes the two witness hash tables. Called exactly once from
* witness_initialize().
*/
static void
witness_init_hash_tables(void)
{
int i;
MPASS(witness_cold);
/* Initialize the hash tables. */
for (i = 0; i < WITNESS_HASH_SIZE; i++)
w_hash.wh_array[i] = NULL;
w_hash.wh_size = WITNESS_HASH_SIZE;
w_hash.wh_count = 0;
/* Initialize the lock order data hash. */
w_lofree = NULL;
for (i = 0; i < WITNESS_LO_DATA_COUNT; i++) {
memset(&w_lodata[i], 0, sizeof(w_lodata[i]));
w_lodata[i].wlod_next = w_lofree;
w_lofree = &w_lodata[i];
}
w_lohash.wloh_size = WITNESS_LO_HASH_SIZE;
w_lohash.wloh_count = 0;
for (i = 0; i < WITNESS_LO_HASH_SIZE; i++)
w_lohash.wloh_array[i] = NULL;
}
static struct witness *
witness_hash_get(const char *key)
{
struct witness *w;
uint32_t hash;
MPASS(key != NULL);
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
hash = witness_hash_djb2(key, 0) % w_hash.wh_size;
w = w_hash.wh_array[hash];
while (w != NULL) {
if (strcmp(w->w_name, key) == 0)
goto out;
w = w->w_hash_next;
}
out:
return (w);
}
static void
witness_hash_put(struct witness *w)
{
uint32_t hash;
MPASS(w != NULL);
MPASS(w->w_name != NULL);
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
KASSERT(witness_hash_get(w->w_name) == NULL,
("%s: trying to add a hash entry that already exists!", __func__));
KASSERT(w->w_hash_next == NULL,
("%s: w->w_hash_next != NULL", __func__));
hash = witness_hash_djb2(w->w_name, 0) % w_hash.wh_size;
w->w_hash_next = w_hash.wh_array[hash];
w_hash.wh_array[hash] = w;
w_hash.wh_count++;
}
static struct witness_lock_order_data *
witness_lock_order_get(struct witness *parent, struct witness *child)
{
struct witness_lock_order_data *data = NULL;
struct witness_lock_order_key key;
unsigned int hash;
MPASS(parent != NULL && child != NULL);
key.from = parent->w_index;
key.to = child->w_index;
WITNESS_INDEX_ASSERT(key.from);
WITNESS_INDEX_ASSERT(key.to);
if ((w_rmatrix[parent->w_index][child->w_index]
& WITNESS_LOCK_ORDER_KNOWN) == 0)
goto out;
hash = witness_hash_djb2((const char*)&key,
sizeof(key)) % w_lohash.wloh_size;
data = w_lohash.wloh_array[hash];
while (data != NULL) {
if (witness_lock_order_key_equal(&data->wlod_key, &key))
break;
data = data->wlod_next;
}
out:
return (data);
}
/*
* Verify that parent and child have a known relationship, are not the same,
* and child is actually a child of parent. This is done without w_mtx
* to avoid contention in the common case.
*/
static int
witness_lock_order_check(struct witness *parent, struct witness *child)
{
if (parent != child &&
w_rmatrix[parent->w_index][child->w_index]
& WITNESS_LOCK_ORDER_KNOWN &&
isitmychild(parent, child))
return (1);
return (0);
}
static int
witness_lock_order_add(struct witness *parent, struct witness *child)
{
struct witness_lock_order_data *data = NULL;
struct witness_lock_order_key key;
unsigned int hash;
MPASS(parent != NULL && child != NULL);
key.from = parent->w_index;
key.to = child->w_index;
WITNESS_INDEX_ASSERT(key.from);
WITNESS_INDEX_ASSERT(key.to);
if (w_rmatrix[parent->w_index][child->w_index]
& WITNESS_LOCK_ORDER_KNOWN)
return (1);
hash = witness_hash_djb2((const char*)&key,
sizeof(key)) % w_lohash.wloh_size;
w_rmatrix[parent->w_index][child->w_index] |= WITNESS_LOCK_ORDER_KNOWN;
data = w_lofree;
if (data == NULL)
return (0);
w_lofree = data->wlod_next;
data->wlod_next = w_lohash.wloh_array[hash];
data->wlod_key = key;
w_lohash.wloh_array[hash] = data;
w_lohash.wloh_count++;
stack_zero(&data->wlod_stack);
stack_save(&data->wlod_stack);
return (1);
}
/* Call this whenever the structure of the witness graph changes. */
static void
witness_increment_graph_generation(void)
{
if (witness_cold == 0)
mtx_assert(&w_mtx, MA_OWNED);
w_generation++;
}
static int
witness_output_drain(void *arg __unused, const char *data, int len)
{
witness_output("%.*s", len, data);
return (len);
}
static void
witness_debugger(int cond, const char *msg)
{
char buf[32];
struct sbuf sb;
struct stack st;
if (!cond)
return;
if (witness_trace) {
sbuf_new(&sb, buf, sizeof(buf), SBUF_FIXEDLEN);
sbuf_set_drain(&sb, witness_output_drain, NULL);
stack_zero(&st);
stack_save(&st);
witness_output("stack backtrace:\n");
stack_sbuf_print_ddb(&sb, &st);
sbuf_finish(&sb);
}
#ifdef KDB
if (witness_kdb)
kdb_enter(KDB_WHY_WITNESS, msg);
#endif
}
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