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blk-mq: Allow blocking queue tag iter callbacks

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commit 530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b upstream.

A recent commit runs tag iterator callbacks under the rcu read lock,
but existing callbacks do not satisfy the non-blocking requirement.
The commit intended to prevent an iterator from accessing a queue that's
being modified. This patch fixes the original issue by taking a queue
reference instead of reading it, which allows callbacks to make blocking
calls.

Fixes: f5bbbbe4d6357 ("blk-mq: sync the update nr_hw_queues with blk_mq_queue_tag_busy_iter")
Acked-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Keith Busch 2018-09-25 10:36:20 -06:00 committed by Greg Kroah-Hartman
parent fa9355afd5
commit 4764810c45
1 changed files with 2 additions and 5 deletions
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7
block/blk-mq-tag.c
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@ -484,11 +484,8 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
/*
* Avoid potential races with things like queue removal.
*/
rcu_read_lock();
if (percpu_ref_is_zero(&q->q_usage_counter)) {
rcu_read_unlock();
if (!percpu_ref_tryget(&q->q_usage_counter))
return;
}
queue_for_each_hw_ctx(q, hctx, i) {
struct blk_mq_tags *tags = hctx->tags;
@ -505,7 +502,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
bt_for_each(hctx, &tags->bitmap_tags, tags->nr_reserved_tags, fn, priv,
false);
}
rcu_read_unlock();
blk_queue_exit(q);
}
static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)