在 2025/8/15 21:17, Ming Lei 写道:
Commit 5989bfe6ac6b ("block: restore two stage elevator switch while
running nr_hw_queue update") reintroduced a lockdep warning by calling
blk_mq_freeze_queue_nomemsave() before switching the I/O scheduler.
The function blk_mq_elv_switch_none() calls elevator_change_done().
Running this while the queue is frozen causes a lockdep warning.
Fix this by reordering the operations: first, switch the I/O scheduler
to 'none', and then freeze the queue. This ensures that elevator_change_done()
is not called on an already frozen queue. And this way is safe because
elevator_set_none() does freeze queue before switching to none.
Also we still have to rely on blk_mq_elv_switch_back() for switching
back, and it has to cover unfrozen queue case.
Cc: Nilay Shroff<nilay@xxxxxxxxxxxxx>
Cc: Yu Kuai<yukuai3@xxxxxxxxxx>
Fixes: 5989bfe6ac6b ("block: restore two stage elevator switch while running nr_hw_queue update")
Signed-off-by: Ming Lei<ming.lei@xxxxxxxxxx>
---
V2:
- fix the issue locally, so patch is simplified
block/blk-mq.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
LGTM
Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>
