6.16-stable review patch. If anyone has any objections, please let me know.
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From: Ming Lei ming.lei@redhat.com
[ Upstream commit 2d82f3bd8910eb65e30bb2a3c9b945bfb3b6d661 ]
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@linux.ibm.com Cc: Yu Kuai yukuai3@huawei.com Fixes: 5989bfe6ac6b ("block: restore two stage elevator switch while running nr_hw_queue update") Signed-off-by: Ming Lei ming.lei@redhat.com Reviewed-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Nilay Shroff nilay@linux.ibm.com Link: https://lore.kernel.org/r/20250815131737.331692-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-mq.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 4cb2f5ca8656..355db0abe44b 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -5031,6 +5031,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, unsigned int memflags; int i; struct xarray elv_tbl, et_tbl; + bool queues_frozen = false;
lockdep_assert_held(&set->tag_list_lock);
@@ -5054,9 +5055,6 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, blk_mq_sysfs_unregister_hctxs(q); }
- list_for_each_entry(q, &set->tag_list, tag_set_list) - blk_mq_freeze_queue_nomemsave(q); - /* * Switch IO scheduler to 'none', cleaning up the data associated * with the previous scheduler. We will switch back once we are done @@ -5066,6 +5064,9 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, if (blk_mq_elv_switch_none(q, &elv_tbl)) goto switch_back;
+ list_for_each_entry(q, &set->tag_list, tag_set_list) + blk_mq_freeze_queue_nomemsave(q); + queues_frozen = true; if (blk_mq_realloc_tag_set_tags(set, nr_hw_queues) < 0) goto switch_back;
@@ -5089,8 +5090,12 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, } switch_back: /* The blk_mq_elv_switch_back unfreezes queue for us. */ - list_for_each_entry(q, &set->tag_list, tag_set_list) + list_for_each_entry(q, &set->tag_list, tag_set_list) { + /* switch_back expects queue to be frozen */ + if (!queues_frozen) + blk_mq_freeze_queue_nomemsave(q); blk_mq_elv_switch_back(q, &elv_tbl, &et_tbl); + }
list_for_each_entry(q, &set->tag_list, tag_set_list) { blk_mq_sysfs_register_hctxs(q);