linux-kernel - [PATCH 5.17 657/772] block: Fix potential deadlock in blk_ia_range_sysfs

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Message-Id: <20220607165008.422498772@linuxfoundation.org>
Date:   Tue,  7 Jun 2022 19:04:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.17 657/772] block: Fix potential deadlock in blk_ia_range_sysfs_show()

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

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@...r.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Link: https://lore.kernel.org/r/20220603021905.1441419-1-damien.lemoal@opensource.wdc.com
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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 = {