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as-iosched: properly protect ioc_gone and ioc count

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If we have multiple tasks freeing io contexts when as-iosched
is being unloaded, we could complete() ioc_gone twice. Fix that by
protecting ioc_gone complete() and clearing with a spinlock for
just that purpose. Doesn't matter from a performance perspective,
since it'll only enter that path when ioc_gone != NULL (when as-iosched
is being rmmod'ed).

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2008-05-29 09:35:22 +02:00
parent 9a11b4ed0e
commit 863fddcb4b
1 changed files with 15 additions and 3 deletions
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18
block/as-iosched.c
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@ -151,6 +151,7 @@ enum arq_state {
static DEFINE_PER_CPU(unsigned long, ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);
static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
static void as_antic_stop(struct as_data *ad);
@ -164,8 +165,19 @@ static void free_as_io_context(struct as_io_context *aic)
{
kfree(aic);
elv_ioc_count_dec(ioc_count);
if (ioc_gone && !elv_ioc_count_read(ioc_count))
complete(ioc_gone);
if (ioc_gone) {
/*
* AS scheduler is exiting, grab exit lock and check
* the pending io context count. If it hits zero,
* complete ioc_gone and set it back to NULL.
*/
spin_lock(&ioc_gone_lock);
if (ioc_gone && !elv_ioc_count_read(ioc_count)) {
complete(ioc_gone);
ioc_gone = NULL;
}
spin_unlock(&ioc_gone_lock);
}
}
static void as_trim(struct io_context *ioc)
@ -1493,7 +1505,7 @@ static void __exit as_exit(void)
/* ioc_gone's update must be visible before reading ioc_count */
smp_wmb();
if (elv_ioc_count_read(ioc_count))
wait_for_completion(ioc_gone);
wait_for_completion(&all_gone);
synchronize_rcu();
}