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Fix taskq_wait_id()

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The existing taskq_wait_id() function can incorrectly block
indefinitely.  Reimplement it more simply using wait_event()
in a similar fashion to taskq_wait_all().

This flaw was uncovered in the context of moving vn_rdwr() to
a taskq.  Previously taskq_wait_id() had no consumers outside
the SPLAT task framework which is why the issue went unnoticed.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Brian Behlendorf 2013-04-29 13:47:59 -07:00
parent ab59be7bc7
commit 99c452bbba
1 changed files with 15 additions and 27 deletions
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42
module/spl/spl-taskq.c
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@ -342,39 +342,27 @@ taskq_find(taskq_t *tq, taskqid_t id, int *active)
SRETURN(NULL);
}
static int
taskq_wait_id_check(taskq_t *tq, taskqid_t id)
{
int active = 0;
int rc;
spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
rc = (taskq_find(tq, id, &active) == NULL);
spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
return (rc);
}
/*
* The taskq_wait_id() function blocks until the passed task id completes.
* This does not guarantee that all lower task id's have completed.
* This does not guarantee that all lower task ids have completed.
*/
void
taskq_wait_id(taskq_t *tq, taskqid_t id)
{
DEFINE_WAIT(wait);
taskq_ent_t *t;
int active = 0;
SENTRY;
ASSERT(tq);
ASSERT(id > 0);
spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags);
t = taskq_find(tq, id, &active);
if (t)
prepare_to_wait(&t->tqent_waitq, &wait, TASK_UNINTERRUPTIBLE);
spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags);
/*
* We rely on the kernels autoremove_wake_function() function to
* remove us from the wait queue in the context of wake_up().
* Once woken the taskq_ent_t pointer must never be accessed.
*/
if (t) {
t = NULL;
schedule();
__set_current_state(TASK_RUNNING);
}
SEXIT;
wait_event(tq->tq_wait_waitq, taskq_wait_id_check(tq, id));
}
EXPORT_SYMBOL(taskq_wait_id);