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| author | Keith Busch <keith.busch@intel.com> | 2018-09-25 18:36:20 +0200 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2018-09-26 04:17:59 +0200 |
| commit | 530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b (patch) | |
| tree | f25bd9aa92fc0042974192d81b705253ddd8c597 | |
| parent | block: use nanosecond resolution for iostat (diff) | |
| download | linux-530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b.tar.xz linux-530ca2c9bd6949c72c9b5cfc330cb3dbccaa3f5b.zip | |
blk-mq: Allow blocking queue tag iter callbacks
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>
| -rw-r--r-- | block/blk-mq-tag.c | 13 |
1 files changed, 4 insertions, 9 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 94e1ed667b6e..41317c50a446 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -322,16 +322,11 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, /* * __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; @@ -347,7 +342,7 @@ void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn, 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 int bt_alloc(struct sbitmap_queue *bt, unsigned int depth, |