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block: don't grab elevator lock during queue initialization

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->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@google.com/

Reported-by: syzbot+4c7e0f9b94ad65811efb@syzkaller.appspotmail.com
Cc: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250403105402.1334206-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2025-04-03 18:54:02 +08:00 committed by Jens Axboe
parent fb58555211
commit 01b91bf14f
1 changed files with 17 additions and 7 deletions
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24
block/blk-mq.c
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@ -4464,14 +4464,12 @@ 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);
@ -4504,7 +4502,19 @@ 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);
@ -4536,7 +4546,7 @@ 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;
@ -5032,7 +5042,7 @@ 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;