From: Damien Le Moal <damien.lemoal@opensource.wdc.com>

Date: Fri, 3 Jun 2022 11:19:05 +0900

Subject: [PATCH] block: Fix potential deadlock in blk_ia_range_sysfs_show()

Git-commit: 41e46b3c2aa24f755b2ae9ec4ce931ba5f0d8532

Patch-mainline: v5.19-rc1

References: jsc#PED-1183

When being read, a sysfs attribute is already protected against removal

with the kobject node active reference counter. As a result, in

blk_ia_range_sysfs_show(), there is no need to take the queue sysfs

lock when reading the value of a range attribute. Using the queue sysfs

lock in this function creates a potential deadlock situation with the

disk removal, something that a lockdep signals with a splat when the

device is removed:

[  760.703551]  Possible unsafe locking scenario:

[  760.703551]

[  760.703554]        CPU0                    CPU1

[  760.703556]        ----                    ----

[  760.703558]   lock(&q->sysfs_lock);

[  760.703565]                                lock(kn->active#385);

[  760.703573]                                lock(&q->sysfs_lock);

[  760.703579]   lock(kn->active#385);

[  760.703587]

[  760.703587]  *** DEADLOCK ***

Solve this by removing the mutex_lock()/mutex_unlock() calls from

blk_ia_range_sysfs_show().

Fixes: a2247f19ee1c ("block: Add independent access ranges support")

Cc: stable@vger.kernel.org

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

Link: https://lore.kernel.org/r/20220603021905.1441419-1-damien.lemoal@opensource.wdc.com

Signed-off-by: Jens Axboe <axboe@kernel.dk>

Acked-by: Hannes Reinecke <hare@suse.com>

---

 block/blk-ia-ranges.c | 7 +------

 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/block/blk-ia-ranges.c b/block/blk-ia-ranges.c

index 18c68d8b9138..56ed48d2954e 100644

--- a/block/blk-ia-ranges.c

+++ b/block/blk-ia-ranges.c

@@ -54,13 +54,8 @@ static ssize_t blk_ia_range_sysfs_show(struct kobject *kobj,

 		container_of(attr, struct blk_ia_range_sysfs_entry, attr);

 	struct blk_independent_access_range *iar =

 		container_of(kobj, struct blk_independent_access_range, kobj);

-	ssize_t ret;

-	mutex_lock(&iar->queue->sysfs_lock);

-	ret = entry->show(iar, buf);

-	mutex_unlock(&iar->queue->sysfs_lock);

-

-	return ret;

+	return entry->show(iar, buf);

 }

 static const struct sysfs_ops blk_ia_range_sysfs_ops = {

-- 

2.35.3