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If callout_stop_safe() noted that the callout is currently executing,

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but next invocation is cancelled while migrating,
sleepq_check_timeout() needs to be informed that the callout is
stopped.  Otherwise the thread switches off CPU and never become
runnable, since running callout could have already raced with us,
while the migrating and cancelled callout could be one which is
expected to set TDP_TIMOFAIL flag for us.  This contradicts with the
expected behaviour of callout_stop() for other callers, which
e.g. decrement references from the callout callbacks.

Add a new flag CS_MIGRBLOCK requesting report of the situation as
'successfully stopped'.

Reviewed by:	jhb (previous version)
Tested by:	cognet, pho
PR:	200992
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D5221
This commit is contained in:
Konstantin Belousov 2016-03-02 18:46:17 +00:00
parent ca8c8dc3eb
commit 5db9ed8062
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=296320
3 changed files with 14 additions and 7 deletions
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10
sys/kern/kern_timeout.c
View File

@ -1155,14 +1155,14 @@ callout_schedule(struct callout *c, int to_ticks)
}
int
_callout_stop_safe(struct callout *c, int safe, void (*drain)(void *))
_callout_stop_safe(struct callout *c, int flags, void (*drain)(void *))
{
struct callout_cpu *cc, *old_cc;
struct lock_class *class;
int direct, sq_locked, use_lock;
int not_on_a_list;
if (safe)
if ((flags & CS_DRAIN) != 0)
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, c->c_lock,
"calling %s", __func__);
@ -1170,7 +1170,7 @@ _callout_stop_safe(struct callout *c, int safe, void (*drain)(void *))
* Some old subsystems don't hold Giant while running a callout_stop(),
* so just discard this check for the moment.
*/
if (!safe && c->c_lock != NULL) {
if ((flags & CS_DRAIN) == 0 && c->c_lock != NULL) {
if (c->c_lock == &Giant.lock_object)
use_lock = mtx_owned(&Giant);
else {
@ -1253,7 +1253,7 @@ _callout_stop_safe(struct callout *c, int safe, void (*drain)(void *))
return (-1);
}
if (safe) {
if ((flags & CS_DRAIN) != 0) {
/*
* The current callout is running (or just
* about to run) and blocking is allowed, so
@ -1370,7 +1370,7 @@ _callout_stop_safe(struct callout *c, int safe, void (*drain)(void *))
cc_exec_drain(cc, direct) = drain;
}
CC_UNLOCK(cc);
return (0);
return ((flags & CS_MIGRBLOCK) != 0);
}
CTR3(KTR_CALLOUT, "failed to stop %p func %p arg %p",
c, c->c_func, c->c_arg);

3
sys/kern/subr_sleepqueue.c
View File

@ -586,7 +586,8 @@ sleepq_check_timeout(void)
* another CPU, so synchronize with it to avoid having it
* accidentally wake up a subsequent sleep.
*/
else if (callout_stop(&td->td_slpcallout) == 0) {
else if (_callout_stop_safe(&td->td_slpcallout, CS_MIGRBLOCK, NULL)
== 0) {
td->td_flags |= TDF_TIMEOUT;
TD_SET_SLEEPING(td);
mi_switch(SW_INVOL | SWT_SLEEPQTIMO, NULL);

8
sys/sys/callout.h
View File

@ -62,6 +62,12 @@ struct callout_handle {
struct callout *callout;
};
/* Flags for callout_stop_safe() */
#define CS_DRAIN 0x0001 /* callout_drain(), wait allowed */
#define CS_MIGRBLOCK 0x0002 /* Block migration, return value
indicates that the callout was
executing */
#ifdef _KERNEL
/*
* Note the flags field is actually *two* fields. The c_flags
@ -81,7 +87,7 @@ struct callout_handle {
*/
#define callout_active(c) ((c)->c_flags & CALLOUT_ACTIVE)
#define callout_deactivate(c) ((c)->c_flags &= ~CALLOUT_ACTIVE)
#define callout_drain(c) _callout_stop_safe(c, 1, NULL)
#define callout_drain(c) _callout_stop_safe(c, CS_DRAIN, NULL)
void callout_init(struct callout *, int);
void _callout_init_lock(struct callout *, struct lock_object *, int);
#define callout_init_mtx(c, mtx, flags) \