freebsd-dev/sys/kern/kern_synch.c
Andriy Gapon 353705930f panic: add a switch and infrastructure for stopping other CPUs in SMP case
Historical behavior of letting other CPUs merily go on is a default for
time being.  The new behavior can be switched on via
kern.stop_scheduler_on_panic tunable and sysctl.

Stopping of the CPUs has (at least) the following benefits:
- more of the system state at panic time is preserved intact
- threads and interrupts do not interfere with dumping of the system
  state

Only one thread runs uninterrupted after panic if stop_scheduler_on_panic
is set.  That thread might call code that is also used in normal context
and that code might use locks to prevent concurrent execution of certain
parts.  Those locks might be held by the stopped threads and would never
be released.  To work around this issue, it was decided that instead of
explicit checks for panic context, we would rather put those checks
inside the locking primitives.

This change has substantial portions written and re-written by attilio
and kib at various times.  Other changes are heavily based on the ideas
and patches submitted by jhb and mdf.  bde has provided many insights
into the details and history of the current code.

The new behavior may cause problems for systems that use a USB keyboard
for interfacing with system console.  This is because of some unusual
locking patterns in the ukbd code which have to be used because on one
hand ukbd is below syscons, but on the other hand it has to interface
with other usb code that uses regular mutexes/Giant for its concurrency
protection.  Dumping to USB-connected disks may also be affected.

PR:			amd64/139614 (at least)
In cooperation with:	attilio, jhb, kib, mdf
Discussed with:		arch@, bde
Tested by:		Eugene Grosbein <eugen@grosbein.net>,
			gnn,
			Steven Hartland <killing@multiplay.co.uk>,
			glebius,
			Andrew Boyer <aboyer@averesystems.com>
			(various versions of the patch)
MFC after:		3 months (or never)
2011-12-11 21:02:01 +00:00

607 lines
16 KiB
C

/*-
* Copyright (c) 1982, 1986, 1990, 1991, 1993
* The Regents of the University of California. All rights reserved.
* (c) UNIX System Laboratories, Inc.
* All or some portions of this file are derived from material licensed
* to the University of California by American Telephone and Telegraph
* Co. or Unix System Laboratories, Inc. and are reproduced herein with
* the permission of UNIX System Laboratories, Inc.
*
* 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.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 THE REGENTS OR CONTRIBUTORS 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.
*
* @(#)kern_synch.c 8.9 (Berkeley) 5/19/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_ktrace.h"
#include "opt_sched.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/condvar.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/sleepqueue.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysproto.h>
#include <sys/vmmeter.h>
#ifdef KTRACE
#include <sys/uio.h>
#include <sys/ktrace.h>
#endif
#include <machine/cpu.h>
#ifdef XEN
#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/pmap.h>
#endif
#define KTDSTATE(td) \
(((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep" : \
((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" : \
((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" : \
((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" : \
((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding")
static void synch_setup(void *dummy);
SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup,
NULL);
int hogticks;
static int pause_wchan;
static struct callout loadav_callout;
struct loadavg averunnable =
{ {0, 0, 0}, FSCALE }; /* load average, of runnable procs */
/*
* Constants for averages over 1, 5, and 15 minutes
* when sampling at 5 second intervals.
*/
static fixpt_t cexp[3] = {
0.9200444146293232 * FSCALE, /* exp(-1/12) */
0.9834714538216174 * FSCALE, /* exp(-1/60) */
0.9944598480048967 * FSCALE, /* exp(-1/180) */
};
/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */
static int fscale __unused = FSCALE;
SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, "");
static void loadav(void *arg);
void
sleepinit(void)
{
hogticks = (hz / 10) * 2; /* Default only. */
init_sleepqueues();
}
/*
* General sleep call. Suspends the current thread until a wakeup is
* performed on the specified identifier. The thread will then be made
* runnable with the specified priority. Sleeps at most timo/hz seconds
* (0 means no timeout). If pri includes PCATCH flag, signals are checked
* before and after sleeping, else signals are not checked. Returns 0 if
* awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a
* signal needs to be delivered, ERESTART is returned if the current system
* call should be restarted if possible, and EINTR is returned if the system
* call should be interrupted by the signal (return EINTR).
*
* The lock argument is unlocked before the caller is suspended, and
* re-locked before _sleep() returns. If priority includes the PDROP
* flag the lock is not re-locked before returning.
*/
int
_sleep(void *ident, struct lock_object *lock, int priority,
const char *wmesg, int timo)
{
struct thread *td;
struct proc *p;
struct lock_class *class;
int catch, flags, lock_state, pri, rval;
WITNESS_SAVE_DECL(lock_witness);
td = curthread;
p = td->td_proc;
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(1, 0);
#endif
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock,
"Sleeping on \"%s\"", wmesg);
KASSERT(timo != 0 || mtx_owned(&Giant) || lock != NULL,
("sleeping without a lock"));
KASSERT(p != NULL, ("msleep1"));
KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
if (priority & PDROP)
KASSERT(lock != NULL && lock != &Giant.lock_object,
("PDROP requires a non-Giant lock"));
if (lock != NULL)
class = LOCK_CLASS(lock);
else
class = NULL;
if (cold || SCHEDULER_STOPPED()) {
/*
* During autoconfiguration, just return;
* don't run any other threads or panic below,
* in case this is the idle thread and already asleep.
* XXX: this used to do "s = splhigh(); splx(safepri);
* splx(s);" to give interrupts a chance, but there is
* no way to give interrupts a chance now.
*/
if (lock != NULL && priority & PDROP)
class->lc_unlock(lock);
return (0);
}
catch = priority & PCATCH;
pri = priority & PRIMASK;
/*
* If we are already on a sleep queue, then remove us from that
* sleep queue first. We have to do this to handle recursive
* sleeps.
*/
if (TD_ON_SLEEPQ(td))
sleepq_remove(td, td->td_wchan);
if (ident == &pause_wchan)
flags = SLEEPQ_PAUSE;
else
flags = SLEEPQ_SLEEP;
if (catch)
flags |= SLEEPQ_INTERRUPTIBLE;
if (priority & PBDRY)
flags |= SLEEPQ_STOP_ON_BDRY;
sleepq_lock(ident);
CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)",
td->td_tid, p->p_pid, td->td_name, wmesg, ident);
if (lock == &Giant.lock_object)
mtx_assert(&Giant, MA_OWNED);
DROP_GIANT();
if (lock != NULL && lock != &Giant.lock_object &&
!(class->lc_flags & LC_SLEEPABLE)) {
WITNESS_SAVE(lock, lock_witness);
lock_state = class->lc_unlock(lock);
} else
/* GCC needs to follow the Yellow Brick Road */
lock_state = -1;
/*
* We put ourselves on the sleep queue and start our timeout
* before calling thread_suspend_check, as we could stop there,
* and a wakeup or a SIGCONT (or both) could occur while we were
* stopped without resuming us. Thus, we must be ready for sleep
* when cursig() is called. If the wakeup happens while we're
* stopped, then td will no longer be on a sleep queue upon
* return from cursig().
*/
sleepq_add(ident, lock, wmesg, flags, 0);
if (timo)
sleepq_set_timeout(ident, timo);
if (lock != NULL && class->lc_flags & LC_SLEEPABLE) {
sleepq_release(ident);
WITNESS_SAVE(lock, lock_witness);
lock_state = class->lc_unlock(lock);
sleepq_lock(ident);
}
if (timo && catch)
rval = sleepq_timedwait_sig(ident, pri);
else if (timo)
rval = sleepq_timedwait(ident, pri);
else if (catch)
rval = sleepq_wait_sig(ident, pri);
else {
sleepq_wait(ident, pri);
rval = 0;
}
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(0, 0);
#endif
PICKUP_GIANT();
if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) {
class->lc_lock(lock, lock_state);
WITNESS_RESTORE(lock, lock_witness);
}
return (rval);
}
int
msleep_spin(void *ident, struct mtx *mtx, const char *wmesg, int timo)
{
struct thread *td;
struct proc *p;
int rval;
WITNESS_SAVE_DECL(mtx);
td = curthread;
p = td->td_proc;
KASSERT(mtx != NULL, ("sleeping without a mutex"));
KASSERT(p != NULL, ("msleep1"));
KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep"));
if (cold || SCHEDULER_STOPPED()) {
/*
* During autoconfiguration, just return;
* don't run any other threads or panic below,
* in case this is the idle thread and already asleep.
* XXX: this used to do "s = splhigh(); splx(safepri);
* splx(s);" to give interrupts a chance, but there is
* no way to give interrupts a chance now.
*/
return (0);
}
sleepq_lock(ident);
CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)",
td->td_tid, p->p_pid, td->td_name, wmesg, ident);
DROP_GIANT();
mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED);
WITNESS_SAVE(&mtx->lock_object, mtx);
mtx_unlock_spin(mtx);
/*
* We put ourselves on the sleep queue and start our timeout.
*/
sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0);
if (timo)
sleepq_set_timeout(ident, timo);
/*
* Can't call ktrace with any spin locks held so it can lock the
* ktrace_mtx lock, and WITNESS_WARN considers it an error to hold
* any spin lock. Thus, we have to drop the sleepq spin lock while
* we handle those requests. This is safe since we have placed our
* thread on the sleep queue already.
*/
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW)) {
sleepq_release(ident);
ktrcsw(1, 0);
sleepq_lock(ident);
}
#endif
#ifdef WITNESS
sleepq_release(ident);
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"",
wmesg);
sleepq_lock(ident);
#endif
if (timo)
rval = sleepq_timedwait(ident, 0);
else {
sleepq_wait(ident, 0);
rval = 0;
}
#ifdef KTRACE
if (KTRPOINT(td, KTR_CSW))
ktrcsw(0, 0);
#endif
PICKUP_GIANT();
mtx_lock_spin(mtx);
WITNESS_RESTORE(&mtx->lock_object, mtx);
return (rval);
}
/*
* pause() delays the calling thread by the given number of system ticks.
* During cold bootup, pause() uses the DELAY() function instead of
* the tsleep() function to do the waiting. The "timo" argument must be
* greater than or equal to zero. A "timo" value of zero is equivalent
* to a "timo" value of one.
*/
int
pause(const char *wmesg, int timo)
{
KASSERT(timo >= 0, ("pause: timo must be >= 0"));
/* silently convert invalid timeouts */
if (timo < 1)
timo = 1;
if (cold) {
/*
* We delay one HZ at a time to avoid overflowing the
* system specific DELAY() function(s):
*/
while (timo >= hz) {
DELAY(1000000);
timo -= hz;
}
if (timo > 0)
DELAY(timo * tick);
return (0);
}
return (tsleep(&pause_wchan, 0, wmesg, timo));
}
/*
* Make all threads sleeping on the specified identifier runnable.
*/
void
wakeup(void *ident)
{
int wakeup_swapper;
sleepq_lock(ident);
wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0);
sleepq_release(ident);
if (wakeup_swapper) {
KASSERT(ident != &proc0,
("wakeup and wakeup_swapper and proc0"));
kick_proc0();
}
}
/*
* Make a thread sleeping on the specified identifier runnable.
* May wake more than one thread if a target thread is currently
* swapped out.
*/
void
wakeup_one(void *ident)
{
int wakeup_swapper;
sleepq_lock(ident);
wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0);
sleepq_release(ident);
if (wakeup_swapper)
kick_proc0();
}
static void
kdb_switch(void)
{
thread_unlock(curthread);
kdb_backtrace();
kdb_reenter();
panic("%s: did not reenter debugger", __func__);
}
/*
* The machine independent parts of context switching.
*/
void
mi_switch(int flags, struct thread *newtd)
{
uint64_t runtime, new_switchtime;
struct thread *td;
struct proc *p;
td = curthread; /* XXX */
THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED);
p = td->td_proc; /* XXX */
KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code"));
#ifdef INVARIANTS
if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td))
mtx_assert(&Giant, MA_NOTOWNED);
#endif
KASSERT(td->td_critnest == 1 || panicstr,
("mi_switch: switch in a critical section"));
KASSERT((flags & (SW_INVOL | SW_VOL)) != 0,
("mi_switch: switch must be voluntary or involuntary"));
KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself"));
/*
* Don't perform context switches from the debugger.
*/
if (kdb_active)
kdb_switch();
if (SCHEDULER_STOPPED())
return;
if (flags & SW_VOL) {
td->td_ru.ru_nvcsw++;
td->td_swvoltick = ticks;
} else
td->td_ru.ru_nivcsw++;
#ifdef SCHED_STATS
SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]);
#endif
/*
* Compute the amount of time during which the current
* thread was running, and add that to its total so far.
*/
new_switchtime = cpu_ticks();
runtime = new_switchtime - PCPU_GET(switchtime);
td->td_runtime += runtime;
td->td_incruntime += runtime;
PCPU_SET(switchtime, new_switchtime);
td->td_generation++; /* bump preempt-detect counter */
PCPU_INC(cnt.v_swtch);
PCPU_SET(switchticks, ticks);
CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)",
td->td_tid, td->td_sched, p->p_pid, td->td_name);
#if (KTR_COMPILE & KTR_SCHED) != 0
if (TD_IS_IDLETHREAD(td))
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle",
"prio:%d", td->td_priority);
else
KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td),
"prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg,
"lockname:\"%s\"", td->td_lockname);
#endif
#ifdef XEN
PT_UPDATES_FLUSH();
#endif
sched_switch(td, newtd, flags);
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running",
"prio:%d", td->td_priority);
CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)",
td->td_tid, td->td_sched, p->p_pid, td->td_name);
/*
* If the last thread was exiting, finish cleaning it up.
*/
if ((td = PCPU_GET(deadthread))) {
PCPU_SET(deadthread, NULL);
thread_stash(td);
}
}
/*
* Change thread state to be runnable, placing it on the run queue if
* it is in memory. If it is swapped out, return true so our caller
* will know to awaken the swapper.
*/
int
setrunnable(struct thread *td)
{
THREAD_LOCK_ASSERT(td, MA_OWNED);
KASSERT(td->td_proc->p_state != PRS_ZOMBIE,
("setrunnable: pid %d is a zombie", td->td_proc->p_pid));
switch (td->td_state) {
case TDS_RUNNING:
case TDS_RUNQ:
return (0);
case TDS_INHIBITED:
/*
* If we are only inhibited because we are swapped out
* then arange to swap in this process. Otherwise just return.
*/
if (td->td_inhibitors != TDI_SWAPPED)
return (0);
/* FALLTHROUGH */
case TDS_CAN_RUN:
break;
default:
printf("state is 0x%x", td->td_state);
panic("setrunnable(2)");
}
if ((td->td_flags & TDF_INMEM) == 0) {
if ((td->td_flags & TDF_SWAPINREQ) == 0) {
td->td_flags |= TDF_SWAPINREQ;
return (1);
}
} else
sched_wakeup(td);
return (0);
}
/*
* Compute a tenex style load average of a quantity on
* 1, 5 and 15 minute intervals.
*/
static void
loadav(void *arg)
{
int i, nrun;
struct loadavg *avg;
nrun = sched_load();
avg = &averunnable;
for (i = 0; i < 3; i++)
avg->ldavg[i] = (cexp[i] * avg->ldavg[i] +
nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT;
/*
* Schedule the next update to occur after 5 seconds, but add a
* random variation to avoid synchronisation with processes that
* run at regular intervals.
*/
callout_reset(&loadav_callout, hz * 4 + (int)(random() % (hz * 2 + 1)),
loadav, NULL);
}
/* ARGSUSED */
static void
synch_setup(void *dummy)
{
callout_init(&loadav_callout, CALLOUT_MPSAFE);
/* Kick off timeout driven events by calling first time. */
loadav(NULL);
}
int
should_yield(void)
{
return (ticks - curthread->td_swvoltick >= hogticks);
}
void
maybe_yield(void)
{
if (should_yield())
kern_yield(PRI_USER);
}
void
kern_yield(int prio)
{
struct thread *td;
td = curthread;
DROP_GIANT();
thread_lock(td);
if (prio == PRI_USER)
prio = td->td_user_pri;
if (prio >= 0)
sched_prio(td, prio);
mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
thread_unlock(td);
PICKUP_GIANT();
}
/*
* General purpose yield system call.
*/
int
sys_yield(struct thread *td, struct yield_args *uap)
{
thread_lock(td);
if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE)
sched_prio(td, PRI_MAX_TIMESHARE);
mi_switch(SW_VOL | SWT_RELINQUISH, NULL);
thread_unlock(td);
td->td_retval[0] = 0;
return (0);
}