dm-bufio: fix sched in atomic context

JIRA: https://issues.redhat.com/browse/RHEL-119009
Upstream Status: kernel/git/torvalds/linux.git

commit b1bf1a7
Author: Sheng Yong <[email protected]>
Date:   Thu Jul 10 14:48:55 2025 +0800

    dm-bufio: fix sched in atomic context

    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]

    Cc: [email protected]      # v6.4+
    Fixes: 450e8de ("dm bufio: improve concurrent IO performance")
    Signed-off-by: Wang Shuai <[email protected]>
    Signed-off-by: Sheng Yong <[email protected]>
    Signed-off-by: Mikulas Patocka <[email protected]>

Signed-off-by: Benjamin Marzinski <[email protected]>

Author: bmarzins

drivers/md/dm-bufio.c

@@ -2742,7 +2742,11 @@ static unsigned long __evict_a_few(unsigned long nr_buffers)
 		__make_buffer_clean(b);
 		__free_buffer_wake(b);
 
-		cond_resched();
+		if (need_resched()) {
+			dm_bufio_unlock(c);
+			cond_resched();
+			dm_bufio_lock(c);
+		}
 	}
 
 	dm_bufio_unlock(c);