[PATCH 5.17 657/772] block: Fix potential deadlock in blk_ia_range_sysfs_show()
From: Greg Kroah-Hartman
Date: Tue Jun 07 2022 - 17:49:54 EST
From: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
commit 41e46b3c2aa24f755b2ae9ec4ce931ba5f0d8532 upstream.
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@xxxxxxxxxxxxxxx
Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220603021905.1441419-1-damien.lemoal@xxxxxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
block/blk-ia-ranges.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
--- a/block/blk-ia-ranges.c
+++ b/block/blk-ia-ranges.c
@@ -54,13 +54,8 @@ static ssize_t blk_ia_range_sysfs_show(s
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 = {