[moderation] [ext4?] KCSAN: data-race in __filemap_add_folio / sync_bdevs (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7dff99b35460 Remove WARN_ALL_UNSEEDED_RANDOM kernel config..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16583f3a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6b32b22d8934c136
dashboard link: https://syzkaller.appspot.com/bug?extid=40f776a7f1b5e8cb4f6c
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [ja...@suse.com 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/30da51958513/disk-7dff99b3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8c35f9221ea0/vmlinux-7dff99b3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/80305f3e627a/bzImage-7dff99b3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+40f776...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __filemap_add_folio / sync_bdevs

read-write to 0xffff88810066b138 of 8 bytes by task 2962 on cpu 1:
__filemap_add_folio+0x671/0x8b0 mm/filemap.c:919
filemap_add_folio+0x1d3/0x350 mm/filemap.c:966
__filemap_get_folio_mpol+0x326/0x680 mm/filemap.c:2016
__filemap_get_folio include/linux/pagemap.h:774 [inline]
grow_dev_folio fs/buffer.c:1047 [inline]
grow_buffers fs/buffer.c:1113 [inline]
__getblk_slow fs/buffer.c:1131 [inline]
bdev_getblk+0x173/0x3f0 fs/buffer.c:1458
__getblk include/linux/buffer_head.h:380 [inline]
jbd2_journal_get_descriptor_buffer+0xce/0x210 fs/jbd2/journal.c:976
jbd2_journal_commit_transaction+0xcc8/0x3420 fs/jbd2/commit.c:610
kjournald2+0x22e/0x3e0 fs/jbd2/journal.c:201
kthread+0x22a/0x280 kernel/kthread.c:467
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff88810066b138 of 8 bytes by task 23265 on cpu 0:
sync_bdevs+0xd3/0x260 block/bdev.c:1285
ksys_sync fs/sync.c:106 [inline]
__ia32_sys_sync+0x8b/0xb0 fs/sync.c:111
x64_sys_call+0x2f3a/0x3020 arch/x86/include/generated/asm/syscalls_64.h:163
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000383 -> 0x0000000000000384

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 23265 Comm: syz.5.6666 Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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