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authorPaolo Valente <paolo.valente@linaro.org>2019-08-07 16:17:54 +0200
committerJens Axboe <axboe@kernel.dk>2019-08-08 07:30:52 -0600
commit3f758e844aa9800eb660d60ee10226fa802594d4 (patch)
tree25fa18af9d966e3f30ad409b51190e61a205fad3 /block/bfq-iosched.c
parent08d383a74948b43eb6e96c86153e63cbf276f1fa (diff)
block, bfq: move update of waker and woken list to queue freeing
Since commit 13a857a4c4e8 ("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 13a857a4c4e8 ("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: 13a857a4c4e8 ("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>
Diffstat (limited to 'block/bfq-iosched.c')
-rw-r--r--block/bfq-iosched.c44
1 files changed, 29 insertions, 15 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index b2009650afc2..5f477501bb3d 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -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 */
}