On 5/19/24 20:38, Yang Yang wrote:
The depth is 62, and the wake_batch is 8. In the following situation,
the task would hang forever.
t1: t2: t3:
blk_mq_get_tag . .
io_schedule . .
elevator_switch .
blk_mq_freeze_queue .
blk_freeze_queue_start .
blk_mq_freeze_queue_wait .
blk_mq_submit_bio
__bio_queue_enter
Fix this issue by waking up all the waiters sleeping on tags after
freezing the queue.
Shouldn't blk_mq_alloc_request() be mentioned in t1 since that is the function
that calls blk_queue_enter()?
diff --git a/block/blk-core.c b/block/blk-core.c
index a16b5abdbbf5..e1eacfad6e5b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -298,8 +298,6 @@ void blk_queue_start_drain(struct request_queue *q)
* prevent I/O from crossing blk_queue_enter().
*/
blk_freeze_queue_start(q);
- if (queue_is_mq(q))
- blk_mq_wake_waiters(q);
/* Make blk_queue_enter() reexamine the DYING flag. */
wake_up_all(&q->mq_freeze_wq);
}
Why has blk_queue_start_drain() been modified? I don't see any reference
in the patch description to blk_queue_start_drain(). Am I perhaps missing
something?
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 4ecb9db62337..9eb3139e713a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -125,8 +125,10 @@ void blk_freeze_queue_start(struct request_queue *q)
if (++q->mq_freeze_depth == 1) {
percpu_ref_kill(&q->q_usage_counter);
mutex_unlock(&q->mq_freeze_lock);
- if (queue_is_mq(q))
+ if (queue_is_mq(q)) {
+ blk_mq_wake_waiters(q);
blk_mq_run_hw_queues(q, false);
+ }
} else {
mutex_unlock(&q->mq_freeze_lock);
}
Why would the above change be necessary? If the blk_queue_enter() call
by blk_mq_alloc_request() succeeds and blk_mq_get_tag() calls
io_schedule(), io_schedule() will be woken up indirectly by the
blk_mq_run_hw_queues() call because that call will free one of the tags
that the io_schedule() call is waiting for.
Thanks,
Bart.
