[moderation] [ext4?] KCSAN: data-race in has_bh_in_lru / invalidate_bh_lrus_cpu (16)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 72c395024dac Merge tag 'docs-7.0' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176657fa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c653aa4dc2fe740b
dashboard link: https://syzkaller.appspot.com/bug?extid=3a0c4dc7649cd539aef7
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [adilger...@dilger.ca linux...@vger.kernel.org linux-...@vger.kernel.org ty...@mit.edu]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c143500d000f/disk-72c39502.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/734418a35433/vmlinux-72c39502.xz
kernel image: https://storage.googleapis.com/syzbot-assets/97548c6e5a9b/bzImage-72c39502.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3a0c4d...@syzkaller.appspotmail.com

EXT4-fs (loop6): unmounting filesystem 00000000-0000-0000-0000-000000000000.
==================================================================
BUG: KCSAN: data-race in has_bh_in_lru / invalidate_bh_lrus_cpu

write to 0xffff888237d27590 of 8 bytes by task 35 on cpu 1:
__invalidate_bh_lrus fs/buffer.c:1530 [inline]
invalidate_bh_lrus_cpu+0x83/0xc0 fs/buffer.c:1575
lru_add_and_bh_lrus_drain mm/swap.c:753 [inline]
lru_add_drain_per_cpu+0x55/0x70 mm/swap.c:772
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4cd/0x9d0 kernel/workqueue.c:3340
worker_thread+0x6bc/0x8b0 kernel/workqueue.c:3421
kthread+0x22a/0x280 kernel/kthread.c:467
ret_from_fork+0x148/0x280 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff888237d27590 of 8 bytes by task 5498 on cpu 0:
has_bh_in_lru+0x35/0x1f0 fs/buffer.c:1552
smp_call_function_many_cond+0x2a9/0xc30 kernel/smp.c:821
on_each_cpu_cond_mask+0x3c/0x80 kernel/smp.c:1043
on_each_cpu_cond include/linux/smp.h:105 [inline]
invalidate_bh_lrus+0x2a/0x30 fs/buffer.c:1561
invalidate_bdev+0x42/0x70 block/bdev.c:100
ext4_put_super+0x624/0x7d0 fs/ext4/super.c:1353
generic_shutdown_super+0xee/0x220 fs/super.c:646
kill_block_super+0x2a/0x70 fs/super.c:1725
ext4_kill_sb+0x42/0x80 fs/ext4/super.c:7449
deactivate_locked_super+0x75/0x1c0 fs/super.c:476
deactivate_super+0x97/0xa0 fs/super.c:509
cleanup_mnt+0x2bb/0x330 fs/namespace.c:1312
__cleanup_mnt+0x19/0x20 fs/namespace.c:1319
task_work_run+0x130/0x1a0 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:44 [inline]
exit_to_user_mode_loop+0x1f7/0x6f0 kernel/entry/common.c:75
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
do_syscall_64+0x1d3/0x2a0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff88811b10c0d0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5498 Comm: syz-executor Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================


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