6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zizhi Wo <redacted>
[ Upstream commit 017dac7670909eaea3eb36e6b3b5a8be9ce0a14d ]
In null_init(), mutex_init(&lock) currently happens after
configfs_register_subsystem(), which exposes the nullb subsystem to
userspace. A racing mkdir() into /sys/kernel/config/nullb/ can reach
null_find_dev_by_name() -> mutex_lock(&lock) before the mutex is
initialized, trigger warning:
[ 123.137788] DEBUG_LOCKS_WARN_ON(lock->magic != lock)
[ 123.137796] WARNING: kernel/locking/mutex.c:159 at mutex_lock+0x171/0x1c0, CPU#13: mkdir/1301
[ 123.140090] Modules linked in: null_blk(+) nft_fib_inet nft_fib_ipv4
......
[ 123.154926] Call Trace:
[ 123.155172] <TASK>
[ 123.155419] ? __pfx_mutex_lock+0x10/0x10
[ 123.156181] ? __pfx__raw_spin_lock+0x10/0x10
[ 123.156571] nullb_group_make_group+0x20/0x100 [null_blk]
[ 123.157011] configfs_mkdir+0x47b/0xc70
[ 123.157337] ? __pfx_configfs_mkdir+0x10/0x10
[ 123.157719] ? may_create_dentry+0x242/0x2e0
[ 123.158061] vfs_mkdir+0x2a9/0x6c0
[ 123.158352] filename_mkdirat+0x3dc/0x500
[ 123.158710] ? __pfx_filename_mkdirat+0x10/0x10
[ 123.159070] ? strncpy_from_user+0x3a/0x1d0
[ 123.159413] __x64_sys_mkdir+0x6b/0x90
[ 123.159760] do_syscall_64+0xea/0x600
Replace the runtime mutex_init(&lock) with a static DEFINE_MUTEX(lock)
declaration to fix this issue.
Fixes: 49c3b9266a71 ("block: null_blk: Improve device creation with configfs")
Suggested-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Zizhi Wo <redacted>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Nilay Shroff <redacted>
Link: https://patch.msgid.link/20260725022509.714271-2-wozizhi@huaweicloud.com (local)
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/block/null_blk/main.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 683e2c61822b0..0790e559c4d19 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -66,7 +66,7 @@ struct nullb_page {
#define NULLB_PAGE_FREE (MAP_SZ - 2)
static LIST_HEAD(nullb_list);
-static struct mutex lock;
+static DEFINE_MUTEX(lock);
static int null_major;
static DEFINE_IDA(nullb_indexes);
static struct blk_mq_tag_set tag_set;@@ -2263,8 +2263,6 @@ static int __init null_init(void)
if (ret)
goto err_tagset;
- mutex_init(&lock);
-
null_major = register_blkdev(0, "nullb");
if (null_major < 0) {
ret = null_major;--
2.53.0