linux-kernel - [PATCH] dm-bufio: fix sched in atomic context

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Message-ID: <20250710064855.239572-1-shengyong1@xiaomi.com>
Date: Thu, 10 Jul 2025 14:48:55 +0800
From: Sheng Yong <shengyong2021@...il.com>
To: agk@...hat.com,
	snitzer@...nel.org,
	mpatocka@...hat.com,
	nhuck@...gle.com
Cc: dm-devel@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	shengyong2021@...il.com,
	Sheng Yong <shengyong1@...omi.com>,
	Wang Shuai <wangshuai12@...omi.com>
Subject: [PATCH] dm-bufio: fix sched in atomic context

From: Sheng Yong <shengyong1@...omi.com>

If "try_verify_in_tasklet" is set for dm-verity, DM_BUFIO_CLIENT_NO_SLEEP
is enabled for dm-bufio. However, when bufio tries to evict buffers, there
is a chance to trigger scheduling in spin_lock_bh, the following warning
is hit:

BUG: sleeping function called from invalid context at drivers/md/dm-bufio.c:2745
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 123, name: kworker/2:2
preempt_count: 201, expected: 0
RCU nest depth: 0, expected: 0
4 locks held by kworker/2:2/123:
 #0: ffff88800a2d1548 ((wq_completion)dm_bufio_cache){....}-{0:0}, at: process_one_work+0xe46/0x1970
 #1: ffffc90000d97d20 ((work_completion)(&dm_bufio_replacement_work)){....}-{0:0}, at: process_one_work+0x763/0x1970
 #2: ffffffff8555b528 (dm_bufio_clients_lock){....}-{3:3}, at: do_global_cleanup+0x1ce/0x710
 #3: ffff88801d5820b8 (&c->spinlock){....}-{2:2}, at: do_global_cleanup+0x2a5/0x710
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 2 UID: 0 PID: 123 Comm: kworker/2:2 Not tainted 6.16.0-rc3-g90548c634bd0 #305 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
Workqueue: dm_bufio_cache do_global_cleanup
Call Trace:
 <TASK>
 dump_stack_lvl+0x53/0x70
 __might_resched+0x360/0x4e0
 do_global_cleanup+0x2f5/0x710
 process_one_work+0x7db/0x1970
 worker_thread+0x518/0xea0
 kthread+0x359/0x690
 ret_from_fork+0xf3/0x1b0
 ret_from_fork_asm+0x1a/0x30
 </TASK>

That can be reproduced by:

  veritysetup format --data-block-size=4096 --hash-block-size=4096 /dev/vda /dev/vdb
  SIZE=$(blockdev --getsz /dev/vda)
  dmsetup create myverity -r --table "0 $SIZE verity 1 /dev/vda /dev/vdb 4096 4096 <data_blocks> 1 sha256 <root_hash> <salt> 1 try_verify_in_tasklet"
  mount /dev/dm-0 /mnt -o ro
  echo 102400 > /sys/module/dm_bufio/parameters/max_cache_size_bytes
  [read files in /mnt]

Fixes: 5721d4e5a9cd ("dm verity: Add optional "try_verify_in_tasklet" feature")
Signed-off-by: Wang Shuai <wangshuai12@...omi.com>
Signed-off-by: Sheng Yong <shengyong1@...omi.com>
---
 drivers/md/dm-bufio.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index ec84ba5e93e5..caf6ae9a8b52 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -2742,7 +2742,9 @@ static unsigned long __evict_a_few(unsigned long nr_buffers)
 		__make_buffer_clean(b);
 		__free_buffer_wake(b);
 
+		dm_bufio_unlock(c);
 		cond_resched();
+		dm_bufio_lock(c);
 	}
 
 	dm_bufio_unlock(c);
-- 
2.43.0