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Condition variable reference counts 

Reference count every entry and exit from the condition variable
functions: cv_wait(), cv_wait_timeout(), cv_signal(), cv_broadcast().

This allows us to safely block in cv_destroy() until all consumers
have been scheduled and are no longer accessing the condition
variable memory.

In addition poison the magic value at the start of cv_destroy() to
ensure there are never any new callers after cv_destroy() is called.
The consumer is responsible for ensuring this never occurs.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Brian Behlendorf 2012-11-05 09:04:50 -08:00
parent 87efc30b27
commit d2733258d0
2 changed files with 26 additions and 9 deletions
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3
include/sys/condvar.h
View File

@ -35,12 +35,13 @@
* calling any of the wait/signal funs, and passed into the wait funs.
*/
#define CV_MAGIC 0x346545f4
#define CV_POISON 0x95
#define CV_DESTROY 0x346545f5
typedef struct {
int cv_magic;
wait_queue_head_t cv_event;
wait_queue_head_t cv_destroy;
atomic_t cv_refs;
atomic_t cv_waiters;
kmutex_t *cv_mutex;
} kcondvar_t;

32
module/spl/spl-condvar.c
View File

@ -48,6 +48,7 @@ __cv_init(kcondvar_t *cvp, char *name, kcv_type_t type, void *arg)
init_waitqueue_head(&cvp->cv_event);
init_waitqueue_head(&cvp->cv_destroy);
atomic_set(&cvp->cv_waiters, 0);
atomic_set(&cvp->cv_refs, 1);
cvp->cv_mutex = NULL;
/* We may be called when there is a non-zero preempt_count or
@ -63,14 +64,15 @@ EXPORT_SYMBOL(__cv_init);
static int
cv_destroy_wakeup(kcondvar_t *cvp)
{
if ((cvp->cv_mutex != NULL) ||
(waitqueue_active(&cvp->cv_event)) ||
(atomic_read(&cvp->cv_waiters) > 0))
return 0;
if (!atomic_read(&cvp->cv_waiters) && !atomic_read(&cvp->cv_refs)) {
ASSERT(cvp->cv_mutex == NULL);
ASSERT(!waitqueue_active(&cvp->cv_event));
return 1;
}
return 0;
}
void
__cv_destroy(kcondvar_t *cvp)
{
@ -78,11 +80,15 @@ __cv_destroy(kcondvar_t *cvp)
ASSERT(cvp);
ASSERT(cvp->cv_magic == CV_MAGIC);
/* Block until all waiters have woken */
cvp->cv_magic = CV_DESTROY;
atomic_dec(&cvp->cv_refs);
/* Block until all waiters are woken and references dropped. */
while (cv_destroy_wakeup(cvp) == 0)
wait_event_timeout(cvp->cv_destroy, cv_destroy_wakeup(cvp), 1);
ASSERT3P(cvp->cv_mutex, ==, NULL);
ASSERT3S(atomic_read(&cvp->cv_refs), ==, 0);
ASSERT3S(atomic_read(&cvp->cv_waiters), ==, 0);
ASSERT3S(waitqueue_active(&cvp->cv_event), ==, 0);
@ -100,6 +106,7 @@ cv_wait_common(kcondvar_t *cvp, kmutex_t *mp, int state)
ASSERT(mp);
ASSERT(cvp->cv_magic == CV_MAGIC);
ASSERT(mutex_owned(mp));
atomic_inc(&cvp->cv_refs);
if (cvp->cv_mutex == NULL)
cvp->cv_mutex = mp;
@ -124,6 +131,7 @@ cv_wait_common(kcondvar_t *cvp, kmutex_t *mp, int state)
}
finish_wait(&cvp->cv_event, &wait);
atomic_dec(&cvp->cv_refs);
SEXIT;
}
@ -157,6 +165,7 @@ __cv_timedwait_common(kcondvar_t *cvp, kmutex_t *mp,
ASSERT(mp);
ASSERT(cvp->cv_magic == CV_MAGIC);
ASSERT(mutex_owned(mp));
atomic_inc(&cvp->cv_refs);
if (cvp->cv_mutex == NULL)
cvp->cv_mutex = mp;
@ -166,8 +175,10 @@ __cv_timedwait_common(kcondvar_t *cvp, kmutex_t *mp,
/* XXX - Does not handle jiffie wrap properly */
time_left = expire_time - jiffies;
if (time_left <= 0)
if (time_left <= 0) {
atomic_dec(&cvp->cv_refs);
SRETURN(-1);
}
prepare_to_wait_exclusive(&cvp->cv_event, &wait, state);
atomic_inc(&cvp->cv_waiters);
@ -186,6 +197,7 @@ __cv_timedwait_common(kcondvar_t *cvp, kmutex_t *mp,
}
finish_wait(&cvp->cv_event, &wait);
atomic_dec(&cvp->cv_refs);
SRETURN(time_left > 0 ? time_left : -1);
}
@ -210,6 +222,7 @@ __cv_signal(kcondvar_t *cvp)
SENTRY;
ASSERT(cvp);
ASSERT(cvp->cv_magic == CV_MAGIC);
atomic_inc(&cvp->cv_refs);
/* All waiters are added with WQ_FLAG_EXCLUSIVE so only one
* waiter will be set runable with each call to wake_up().
@ -218,6 +231,7 @@ __cv_signal(kcondvar_t *cvp)
if (atomic_read(&cvp->cv_waiters) > 0)
wake_up(&cvp->cv_event);
atomic_dec(&cvp->cv_refs);
SEXIT;
}
EXPORT_SYMBOL(__cv_signal);
@ -225,15 +239,17 @@ EXPORT_SYMBOL(__cv_signal);
void
__cv_broadcast(kcondvar_t *cvp)
{
SENTRY;
ASSERT(cvp);
ASSERT(cvp->cv_magic == CV_MAGIC);
SENTRY;
atomic_inc(&cvp->cv_refs);
/* Wake_up_all() will wake up all waiters even those which
* have the WQ_FLAG_EXCLUSIVE flag set. */
if (atomic_read(&cvp->cv_waiters) > 0)
wake_up_all(&cvp->cv_event);
atomic_dec(&cvp->cv_refs);
SEXIT;
}
EXPORT_SYMBOL(__cv_broadcast);