->elevator_lock depends on queue freeze lock, see block/blk-sysfs.c. queue freeze lock depends on fs_reclaim. So don't grab elevator lock during queue initialization which needs to call kmalloc(GFP_KERNEL), and we can cut the dependency between ->elevator_lock and fs_reclaim, then the lockdep warning can be killed. This way is safe because elevator setting isn't ready to run during queue initialization. There isn't such issue in __blk_mq_update_nr_hw_queues() because memalloc_noio_save() is called before acquiring elevator lock. Fixes the following lockdep warning: https://lore.kernel.org/linux-block/67e6b425.050a0220.2f068f.007b.GAE@xxxxxxxxxx/ Reported-by: syzbot+4c7e0f9b94ad65811efb@xxxxxxxxxxxxxxxxxxxxxxxxx Cc: Nilay Shroff <nilay@xxxxxxxxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/blk-mq.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index ae8494d88897..d7a103dc258b 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -4465,14 +4465,12 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx( return NULL; } -static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, - struct request_queue *q) +static void __blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, + struct request_queue *q) { struct blk_mq_hw_ctx *hctx; unsigned long i, j; - /* protect against switching io scheduler */ - mutex_lock(&q->elevator_lock); for (i = 0; i < set->nr_hw_queues; i++) { int old_node; int node = blk_mq_get_hctx_node(set, i); @@ -4505,7 +4503,19 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, xa_for_each_start(&q->hctx_table, j, hctx, j) blk_mq_exit_hctx(q, set, hctx, j); - mutex_unlock(&q->elevator_lock); +} + +static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, + struct request_queue *q, bool lock) +{ + if (lock) { + /* protect against switching io scheduler */ + mutex_lock(&q->elevator_lock); + __blk_mq_realloc_hw_ctxs(set, q); + mutex_unlock(&q->elevator_lock); + } else { + __blk_mq_realloc_hw_ctxs(set, q); + } /* unregister cpuhp callbacks for exited hctxs */ blk_mq_remove_hw_queues_cpuhp(q); @@ -4537,7 +4547,7 @@ int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set, xa_init(&q->hctx_table); - blk_mq_realloc_hw_ctxs(set, q); + blk_mq_realloc_hw_ctxs(set, q, false); if (!q->nr_hw_queues) goto err_hctxs; @@ -5033,7 +5043,7 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, fallback: blk_mq_update_queue_map(set); list_for_each_entry(q, &set->tag_list, tag_set_list) { - blk_mq_realloc_hw_ctxs(set, q); + blk_mq_realloc_hw_ctxs(set, q, true); if (q->nr_hw_queues != set->nr_hw_queues) { int i = prev_nr_hw_queues; -- 2.47.0
