blk-mq: reset queue state on scheduler teardown

We observed I/O timeouts with requests stalled in per-CPU software
queues.

The affected queue had no elevator, but QUEUE_FLAG_SQ_SCHED remained
set. A failed elevator switch can leave this state when falling back to
none without clearing the flag. With empty hctx dispatch lists, a
queue-wide restart on CPU4 would skip requests pending in ctx5/ctx7:

CPU4: blk_mq_run_hw_queues(q)
  sq_hctx = hctx4
  hctx4: no pending requests   -> selected
  hctx5: 9 reads in ctx5       -> skipped
  hctx7: 3 writes in ctx7      -> skipped

The pending requests may remain undispatched until another event runs
their hardware queues.

Clear the flag and restore nr_requests and async_depth to the driver
queue depth in the common scheduler teardown path, covering both
scheduler exit and failed initialization.

Fixes: 4d337cebcb1c ("blk-mq: avoid to touch q->elevator without any protection")
Assisted-by: LLM
Signed-off-by: Jianan Huang <jnhuang95@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20261023092611.116795-1-jnhuang95@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions