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block: fix nr_hw_queue update racing with disk addition/removal

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The nr_hw_queue update could potentially race with disk addtion/removal
while registering/unregistering hctx sysfs files. The __blk_mq_update_
nr_hw_queues() runs with q->tag_list_lock held and so to avoid it racing
with disk addition/removal we should acquire q->tag_list_lock while
registering/unregistering hctx sysfs files.

With this patch, blk_mq_sysfs_register() (called during disk addition)
and blk_mq_sysfs_unregister() (called during disk removal) now runs
with q->tag_list_lock held so that it avoids racing with __blk_mq_update
_nr_hw_queues().

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20250128143436.874357-3-nilay@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Nilay Shroff 2025-01-28 20:04:14 +05:30 • committed by Jens Axboe
parent fe66286086
commit 14ef49657f
1 changed files with 9 additions and 8 deletions
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17
block/blk-mq-sysfs.c
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@ -225,25 +225,25 @@ int blk_mq_sysfs_register(struct gendisk *disk)
ret = kobject_add(q->mq_kobj, &disk_to_dev(disk)->kobj, "mq");
if (ret < 0)
goto out;
return ret;
kobject_uevent(q->mq_kobj, KOBJ_ADD);
mutex_lock(&q->tag_set->tag_list_lock);
queue_for_each_hw_ctx(q, hctx, i) {
ret = blk_mq_register_hctx(hctx);
if (ret)
goto unreg;
goto out_unreg;
}
mutex_unlock(&q->tag_set->tag_list_lock);
return 0;
out:
return ret;
unreg:
out_unreg:
queue_for_each_hw_ctx(q, hctx, j) {
if (j < i)
blk_mq_unregister_hctx(hctx);
}
mutex_unlock(&q->tag_set->tag_list_lock);
kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
kobject_del(q->mq_kobj);
@ -256,9 +256,10 @@ void blk_mq_sysfs_unregister(struct gendisk *disk)
struct blk_mq_hw_ctx *hctx;
unsigned long i;
mutex_lock(&q->tag_set->tag_list_lock);
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_unregister_hctx(hctx);
mutex_unlock(&q->tag_set->tag_list_lock);
kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
kobject_del(q->mq_kobj);