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From:   Rafael Mendonca <rafaelmendsr@gmail.com>
To:     Jens Axboe <axboe@kernel.dk>, Hannes Reinecke <hare@suse.de>
Cc:     Rafael Mendonca <rafaelmendsr@gmail.com>,
        syzbot+31c9594f6e43b9289b25@syzkaller.appspotmail.com,
        Hillf Danton <hdanton@sina.com>, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] block: Do not call blk_put_queue() if gendisk allocation fails
Date:   Thu, 11 Aug 2022 20:23:37 -0300
Message-Id: <20220811232338.254673-1-rafaelmendsr@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Commit 6f8191fdf41d ("block: simplify disk shutdown") removed the call
to blk_get_queue() during gendisk allocation but missed to remove the
corresponding cleanup code blk_put_queue() for it. Thus, if the gendisk
allocation fails, the request_queue refcount gets decremented and
reaches 0, causing blk_mq_release() to be called with a hctx still
alive. That triggers a WARNING report, as found by syzkaller:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 23016 at block/blk-mq.c:3881
blk_mq_release+0xf8/0x3e0 block/blk-mq.c:3881
[...] stripped
RIP: 0010:blk_mq_release+0xf8/0x3e0 block/blk-mq.c:3881
[...] stripped
Call Trace:
 <TASK>
 blk_release_queue+0x153/0x270 block/blk-sysfs.c:780
 kobject_cleanup lib/kobject.c:673 [inline]
 kobject_release lib/kobject.c:704 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1c8/0x540 lib/kobject.c:721
 __alloc_disk_node+0x4f7/0x610 block/genhd.c:1388
 __blk_mq_alloc_disk+0x13b/0x1f0 block/blk-mq.c:3961
 loop_add+0x3e2/0xaf0 drivers/block/loop.c:1978
 loop_control_ioctl+0x133/0x620 drivers/block/loop.c:2150
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
[...] stripped

Fixes: 6f8191fdf41d ("block: simplify disk shutdown")
Reported-by: syzbot+31c9594f6e43b9289b25@syzkaller.appspotmail.com
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
---
 block/genhd.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/block/genhd.c b/block/genhd.c
index b901fea1d55a..d36fabf0abc1 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1341,7 +1341,7 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 
 	disk = kzalloc_node(sizeof(struct gendisk), GFP_KERNEL, node_id);
 	if (!disk)
-		goto out_put_queue;
+		return NULL;
 
 	if (bioset_init(&disk->bio_split, BIO_POOL_SIZE, 0, 0))
 		goto out_free_disk;
@@ -1390,8 +1390,6 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 	bioset_exit(&disk->bio_split);
 out_free_disk:
 	kfree(disk);
-out_put_queue:
-	blk_put_queue(q);
 	return NULL;
 }
 
-- 
2.34.1