3f08bd8bce
implementation is by no means perfect as far as some of the algorithms that it uses and the fact that it is missing some functionality (try locks and upgrades/downgrades are not there yet), however it does seem to work in my local testing. There is more detail in the comments in the code, but the short version follows. A reader/writer lock is very much like a regular mutex: it cannot be held across a voluntary sleep; it can be acquired in an interrupt thread; if the lock is held by a writer then the priority of any threads that block on the lock will be lent to the owner; the simple case lock operations all are done in a single atomic op. It also shares some similiarities with sx locks: it supports reader/writer semantics (multiple readers, but single writers); readers are allowed to recurse, but writers are not. We can extend this implementation further by either improving algorithms or adding new functionality, but this should at least give us a base to work with now. Reviewed by: arch (in theory) Tested on: i386 (4 cpu box with a kernel module that used 4 threads that randomly chose between read locks and write locks that ran w/o panicing for over a day solid. It usually panic'd within a few seconds when there were bugs during testing. :) The kernel module source is available on request.)
329 lines
12 KiB
C
329 lines
12 KiB
C
/*-
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* Copyright (c) 1997 Berkeley Software Design, Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Berkeley Software Design Inc's name may not be used to endorse or
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* promote products derived from this software without specific prior
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* written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* from BSDI $Id: mutex.h,v 2.7.2.35 2000/04/27 03:10:26 cp Exp $
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* $FreeBSD$
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*/
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#ifndef _SYS_LOCK_H_
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#define _SYS_LOCK_H_
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#include <sys/queue.h>
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#include <sys/_lock.h>
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struct thread;
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/*
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* Lock classes. Each lock has a class which describes characteristics
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* common to all types of locks of a given class.
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*
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* Spin locks in general must always protect against preemption, as it is
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* an error to perform any type of context switch while holding a spin lock.
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* Also, for an individual lock to be recursable, its class must allow
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* recursion and the lock itself must explicitly allow recursion.
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*/
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struct lock_class {
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const char *lc_name;
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u_int lc_flags;
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void (*lc_ddb_show)(struct lock_object *lock);
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};
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#define LC_SLEEPLOCK 0x00000001 /* Sleep lock. */
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#define LC_SPINLOCK 0x00000002 /* Spin lock. */
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#define LC_SLEEPABLE 0x00000004 /* Sleeping allowed with this lock. */
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#define LC_RECURSABLE 0x00000008 /* Locks of this type may recurse. */
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#define LC_UPGRADABLE 0x00000010 /* Upgrades and downgrades permitted. */
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#define LO_CLASSFLAGS 0x0000ffff /* Class specific flags. */
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#define LO_INITIALIZED 0x00010000 /* Lock has been initialized. */
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#define LO_WITNESS 0x00020000 /* Should witness monitor this lock. */
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#define LO_QUIET 0x00040000 /* Don't log locking operations. */
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#define LO_RECURSABLE 0x00080000 /* Lock may recurse. */
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#define LO_SLEEPABLE 0x00100000 /* Lock may be held while sleeping. */
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#define LO_UPGRADABLE 0x00200000 /* Lock may be upgraded/downgraded. */
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#define LO_DUPOK 0x00400000 /* Don't check for duplicate acquires */
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#define LO_ENROLLPEND 0x00800000 /* On the pending enroll list. */
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#define LO_CLASSMASK 0x0f000000 /* Class index bitmask. */
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/*
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* Lock classes are statically assigned an index into the gobal lock_classes
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* array. Debugging code looks up the lock class for a given lock object
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* by indexing the array.
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*/
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#define LO_CLASSSHIFT 24
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#define LO_CLASSINDEX(lock) ((((lock)->lo_flags) & LO_CLASSMASK) >> LO_CLASSSHIFT)
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#define LOCK_CLASS(lock) (lock_classes[LO_CLASSINDEX((lock))])
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#define LOCK_CLASS_MAX (LO_CLASSMASK >> LO_CLASSSHIFT)
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#define LI_RECURSEMASK 0x0000ffff /* Recursion depth of lock instance. */
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#define LI_EXCLUSIVE 0x00010000 /* Exclusive lock instance. */
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/*
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* Option flags passed to lock operations that witness also needs to know
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* about or that are generic across all locks.
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*/
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#define LOP_NEWORDER 0x00000001 /* Define a new lock order. */
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#define LOP_QUIET 0x00000002 /* Don't log locking operations. */
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#define LOP_TRYLOCK 0x00000004 /* Don't check lock order. */
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#define LOP_EXCLUSIVE 0x00000008 /* Exclusive lock. */
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#define LOP_DUPOK 0x00000010 /* Don't check for duplicate acquires */
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/* Flags passed to witness_assert. */
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#define LA_UNLOCKED 0x00000000 /* Lock is unlocked. */
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#define LA_LOCKED 0x00000001 /* Lock is at least share locked. */
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#define LA_SLOCKED 0x00000002 /* Lock is exactly share locked. */
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#define LA_XLOCKED 0x00000004 /* Lock is exclusively locked. */
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#define LA_RECURSED 0x00000008 /* Lock is recursed. */
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#define LA_NOTRECURSED 0x00000010 /* Lock is not recursed. */
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#ifdef _KERNEL
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/*
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* Lock instances. A lock instance is the data associated with a lock while
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* it is held by witness. For example, a lock instance will hold the
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* recursion count of a lock. Lock instances are held in lists. Spin locks
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* are held in a per-cpu list while sleep locks are held in per-process list.
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*/
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struct lock_instance {
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struct lock_object *li_lock;
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const char *li_file; /* File and line of last acquire. */
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int li_line;
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u_int li_flags; /* Recursion count and LI_* flags. */
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};
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/*
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* A simple list type used to build the list of locks held by a process
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* or CPU. We can't simply embed the list in struct lock_object since a
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* lock may be held by more than one process if it is a shared lock. Locks
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* are added to the head of the list, so we fill up each list entry from
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* "the back" logically. To ease some of the arithmetic, we actually fill
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* in each list entry the normal way (childer[0] then children[1], etc.) but
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* when we traverse the list we read children[count-1] as the first entry
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* down to children[0] as the final entry.
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*/
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#define LOCK_NCHILDREN 3
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struct lock_list_entry {
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struct lock_list_entry *ll_next;
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struct lock_instance ll_children[LOCK_NCHILDREN];
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u_int ll_count;
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};
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/*
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* If any of WITNESS, INVARIANTS, or KTR_LOCK KTR tracing has been enabled,
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* then turn on LOCK_DEBUG. When this option is on, extra debugging
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* facilities such as tracking the file and line number of lock operations
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* are enabled. Also, mutex locking operations are not inlined to avoid
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* bloat from all the extra debugging code. We also have to turn on all the
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* calling conventions for this debugging code in modules so that modules can
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* work with both debug and non-debug kernels.
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*/
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#if defined(KLD_MODULE) || defined(WITNESS) || defined(INVARIANTS) || defined(INVARIANT_SUPPORT) || defined(KTR) || defined(MUTEX_PROFILING)
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#define LOCK_DEBUG 1
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#else
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#define LOCK_DEBUG 0
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#endif
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/*
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* In the LOCK_DEBUG case, use the filename and line numbers for debugging
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* operations. Otherwise, use default values to avoid the unneeded bloat.
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*/
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#if LOCK_DEBUG > 0
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#define LOCK_FILE __FILE__
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#define LOCK_LINE __LINE__
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#else
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#define LOCK_FILE NULL
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#define LOCK_LINE 0
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#endif
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/*
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* Macros for KTR_LOCK tracing.
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*
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* opname - name of this operation (LOCK/UNLOCK/SLOCK, etc.)
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* lo - struct lock_object * for this lock
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* flags - flags passed to the lock operation
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* recurse - this locks recursion level (or 0 if class is not recursable)
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* result - result of a try lock operation
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* file - file name
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* line - line number
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*/
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#define LOCK_LOG_TEST(lo, flags) \
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(((flags) & LOP_QUIET) == 0 && ((lo)->lo_flags & LO_QUIET) == 0)
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#define LOCK_LOG_LOCK(opname, lo, flags, recurse, file, line) do { \
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if (LOCK_LOG_TEST((lo), (flags))) \
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CTR5(KTR_LOCK, opname " (%s) %s r = %d at %s:%d", \
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LOCK_CLASS(lo)->lc_name, (lo)->lo_name, \
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(u_int)(recurse), (file), (line)); \
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} while (0)
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#define LOCK_LOG_TRY(opname, lo, flags, result, file, line) do { \
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if (LOCK_LOG_TEST((lo), (flags))) \
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CTR5(KTR_LOCK, "TRY_" opname " (%s) %s result=%d at %s:%d",\
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LOCK_CLASS(lo)->lc_name, (lo)->lo_name, \
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(u_int)(result), (file), (line)); \
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} while (0)
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#define LOCK_LOG_INIT(lo, flags) do { \
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if (LOCK_LOG_TEST((lo), (flags))) \
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CTR4(KTR_LOCK, "%s: %p (%s) %s", __func__, (lo), \
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LOCK_CLASS(lo)->lc_name, (lo)->lo_name); \
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} while (0)
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#define LOCK_LOG_DESTROY(lo, flags) LOCK_LOG_INIT(lo, flags)
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#define lock_initalized(lo) ((lo)->lo_flags & LO_INITIALIZED)
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/*
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* Helpful macros for quickly coming up with assertions with informative
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* panic messages.
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*/
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#define MPASS(ex) MPASS4(ex, #ex, __FILE__, __LINE__)
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#define MPASS2(ex, what) MPASS4(ex, what, __FILE__, __LINE__)
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#define MPASS3(ex, file, line) MPASS4(ex, #ex, file, line)
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#define MPASS4(ex, what, file, line) \
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KASSERT((ex), ("Assertion %s failed at %s:%d", what, file, line))
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extern struct lock_class lock_class_mtx_sleep;
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extern struct lock_class lock_class_mtx_spin;
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extern struct lock_class lock_class_sx;
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extern struct lock_class lock_class_rw;
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extern struct lock_class *lock_classes[];
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void lock_init(struct lock_object *lock, struct lock_class *class,
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const char *name, const char *type, int flags);
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void lock_destroy(struct lock_object *lock);
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void spinlock_enter(void);
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void spinlock_exit(void);
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void witness_init(struct lock_object *);
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void witness_destroy(struct lock_object *);
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int witness_defineorder(struct lock_object *, struct lock_object *);
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void witness_checkorder(struct lock_object *, int, const char *, int);
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void witness_lock(struct lock_object *, int, const char *, int);
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void witness_upgrade(struct lock_object *, int, const char *, int);
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void witness_downgrade(struct lock_object *, int, const char *, int);
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void witness_unlock(struct lock_object *, int, const char *, int);
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void witness_save(struct lock_object *, const char **, int *);
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void witness_restore(struct lock_object *, const char *, int);
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int witness_list_locks(struct lock_list_entry **);
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int witness_warn(int, struct lock_object *, const char *, ...);
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void witness_assert(struct lock_object *, int, const char *, int);
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void witness_display_spinlock(struct lock_object *, struct thread *);
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int witness_line(struct lock_object *);
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const char *witness_file(struct lock_object *);
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#ifdef WITNESS
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/* Flags for witness_warn(). */
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#define WARN_GIANTOK 0x01 /* Giant is exempt from this check. */
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#define WARN_PANIC 0x02 /* Panic if check fails. */
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#define WARN_SLEEPOK 0x04 /* Sleepable locks are exempt from check. */
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#define WITNESS_INIT(lock) \
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witness_init((lock))
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#define WITNESS_DESTROY(lock) \
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witness_destroy(lock)
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#define WITNESS_CHECKORDER(lock, flags, file, line) \
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witness_checkorder((lock), (flags), (file), (line))
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#define WITNESS_DEFINEORDER(lock1, lock2) \
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witness_defineorder((struct lock_object *)(lock1), \
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(struct lock_object *)(lock2))
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#define WITNESS_LOCK(lock, flags, file, line) \
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witness_lock((lock), (flags), (file), (line))
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#define WITNESS_UPGRADE(lock, flags, file, line) \
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witness_upgrade((lock), (flags), (file), (line))
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#define WITNESS_DOWNGRADE(lock, flags, file, line) \
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witness_downgrade((lock), (flags), (file), (line))
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#define WITNESS_UNLOCK(lock, flags, file, line) \
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witness_unlock((lock), (flags), (file), (line))
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#define WITNESS_CHECK(flags, lock, fmt, ...) \
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witness_warn((flags), (lock), (fmt), ## __VA_ARGS__)
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#define WITNESS_WARN(flags, lock, fmt, ...) \
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witness_warn((flags), (lock), (fmt), ## __VA_ARGS__)
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#define WITNESS_SAVE_DECL(n) \
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const char * __CONCAT(n, __wf); \
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int __CONCAT(n, __wl)
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#define WITNESS_SAVE(lock, n) \
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witness_save((lock), &__CONCAT(n, __wf), &__CONCAT(n, __wl))
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#define WITNESS_RESTORE(lock, n) \
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witness_restore((lock), __CONCAT(n, __wf), __CONCAT(n, __wl))
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#define WITNESS_FILE(lock) \
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witness_file(lock)
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#define WITNESS_LINE(lock) \
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witness_line(lock)
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#else /* WITNESS */
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#define WITNESS_INIT(lock)
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#define WITNESS_DESTROY(lock)
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#define WITNESS_DEFINEORDER(lock1, lock2) 0
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#define WITNESS_CHECKORDER(lock, flags, file, line)
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#define WITNESS_LOCK(lock, flags, file, line)
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#define WITNESS_UPGRADE(lock, flags, file, line)
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#define WITNESS_DOWNGRADE(lock, flags, file, line)
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#define WITNESS_UNLOCK(lock, flags, file, line)
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#define WITNESS_CHECK(flags, lock, fmt, ...) 0
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#define WITNESS_WARN(flags, lock, fmt, ...)
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#define WITNESS_SAVE_DECL(n)
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#define WITNESS_SAVE(lock, n)
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#define WITNESS_RESTORE(lock, n)
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#define WITNESS_FILE(lock) ("?")
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#define WITNESS_LINE(lock) (0)
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#endif /* WITNESS */
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/*
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* Helper macros to allow developers to add explicit lock order checks
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* wherever they please without having to actually grab a lock to do so.
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*/
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#define witness_check_mutex(m) \
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WITNESS_CHECKORDER(&(m)->mtx_object, LOP_EXCLUSIVE, LOCK_FILE, \
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LOCK_LINE)
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#define witness_check_shared_sx(sx) \
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WITNESS_CHECKORDER(&(sx)->sx_object, 0, LOCK_FILE, LOCK_LINE)
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#define witness_check_exclusive_sx(sx) \
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WITNESS_CHECKORDER(&(sx)->sx_object, LOP_EXCLUSIVE, LOCK_FILE, \
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LOCK_LINE)
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#endif /* _KERNEL */
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#endif /* _SYS_LOCK_H_ */
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