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Message-Id: <20200411115419.774992055@linuxfoundation.org>
Date: Sat, 11 Apr 2020 14:08:49 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Jianchao Wang <jianchao.w.wang@...cle.com>,
Keith Busch <keith.busch@...el.com>,
Jens Axboe <axboe@...nel.dk>,
Giuliano Procida <gprocida@...gle.com>
Subject: [PATCH 4.9 10/32] blk-mq: Allow blocking queue tag iter callbacks
From: Keith Busch <keith.busch@...el.com>
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@...cle.com>
Signed-off-by: Keith Busch <keith.busch@...el.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Giuliano Procida <gprocida@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
block/blk-mq-tag.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -338,16 +338,11 @@ void blk_mq_queue_tag_busy_iter(struct r
/*
* __blk_mq_update_nr_hw_queues will update the nr_hw_queues and
- * queue_hw_ctx after freeze the queue. So we could use q_usage_counter
- * to avoid race with it. __blk_mq_update_nr_hw_queues will users
- * synchronize_rcu to ensure all of the users go out of the critical
- * section below and see zeroed q_usage_counter.
+ * queue_hw_ctx after freeze the queue, so we use q_usage_counter
+ * to avoid race with it.
*/
- 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;
@@ -363,7 +358,7 @@ void blk_mq_queue_tag_busy_iter(struct r
bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
}
- rcu_read_unlock();
+ blk_queue_exit(q);
}
static unsigned int bt_unused_tags(const struct sbitmap_queue *bt)
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