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block, bfq: move update of waker and woken list to queue freeing 

Since commit 13a857a4c4 ("block, bfq: detect wakers and
unconditionally inject their I/O"), every bfq_queue has a pointer to a
waker bfq_queue and a list of the bfq_queues it may wake. In this
respect, when a bfq_queue, say Q, remains with no I/O source attached
to it, Q cannot be woken by any other bfq_queue, and cannot wake any
other bfq_queue. Then Q must be removed from the woken list of its
possible waker bfq_queue, and all bfq_queues in the woken list of Q
must stop having a waker bfq_queue.

Q remains with no I/O source in two cases: when the last process
associated with Q exits or when such a process gets associated with a
different bfq_queue. Unfortunately, commit 13a857a4c4 ("block, bfq:
detect wakers and unconditionally inject their I/O") performed the
above updates only in the first case.

This commit fixes this bug by moving these updates to when Q gets
freed. This is a simple and safe way to handle all cases, as both the
above events, process exit and re-association, lead to Q being freed
soon, and because dangling references would come out only after Q gets
freed (if no update were performed).

Fixes: 13a857a4c4 ("block, bfq: detect wakers and unconditionally inject their I/O")
Reported-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2019-08-07 16:17:54 +02:00 committed by Jens Axboe
parent 08d383a749
commit 3f758e844a
1 changed files with 29 additions and 15 deletions
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44
block/bfq-iosched.c
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@ -4765,6 +4765,8 @@ static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
*/
void bfq_put_queue(struct bfq_queue *bfqq)
{
struct bfq_queue *item;
struct hlist_node *n;
#ifdef CONFIG_BFQ_GROUP_IOSCHED
struct bfq_group *bfqg = bfqq_group(bfqq);
#endif
@ -4809,6 +4811,33 @@ void bfq_put_queue(struct bfq_queue *bfqq)
bfqq->bfqd->burst_size--;
}
/*
* bfqq does not exist any longer, so it cannot be woken by
* any other queue, and cannot wake any other queue. Then bfqq
* must be removed from the woken list of its possible waker
* queue, and all queues in the woken list of bfqq must stop
* having a waker queue. Strictly speaking, these updates
* should be performed when bfqq remains with no I/O source
* attached to it, which happens before bfqq gets freed. In
* particular, this happens when the last process associated
* with bfqq exits or gets associated with a different
* queue. However, both events lead to bfqq being freed soon,
* and dangling references would come out only after bfqq gets
* freed. So these updates are done here, as a simple and safe
* way to handle all cases.
*/
/* remove bfqq from woken list */
if (!hlist_unhashed(&bfqq->woken_list_node))
hlist_del_init(&bfqq->woken_list_node);
/* reset waker for all queues in woken list */
hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
woken_list_node) {
item->waker_bfqq = NULL;
bfq_clear_bfqq_has_waker(item);
hlist_del_init(&item->woken_list_node);
}
if (bfqq->bfqd && bfqq->bfqd->last_completed_rq_bfqq == bfqq)
bfqq->bfqd->last_completed_rq_bfqq = NULL;
@ -4839,9 +4868,6 @@ static void bfq_put_cooperator(struct bfq_queue *bfqq)
static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
{
struct bfq_queue *item;
struct hlist_node *n;
if (bfqq == bfqd->in_service_queue) {
__bfq_bfqq_expire(bfqd, bfqq, BFQQE_BUDGET_TIMEOUT);
bfq_schedule_dispatch(bfqd);
@ -4851,18 +4877,6 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
bfq_put_cooperator(bfqq);
/* remove bfqq from woken list */
if (!hlist_unhashed(&bfqq->woken_list_node))
hlist_del_init(&bfqq->woken_list_node);
/* reset waker for all queues in woken list */
hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
woken_list_node) {
item->waker_bfqq = NULL;
bfq_clear_bfqq_has_waker(item);
hlist_del_init(&item->woken_list_node);
}
bfq_put_queue(bfqq); /* release process reference */
}