[moderation] [exfat?] KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode (13)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e7aa57247700 Merge tag 'spi-fix-v6.19-rc8' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1114965a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=c77c6c4a4e6c30fb8ea4
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [hiro...@mail.parknet.co.jp linki...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org sj155...@samsung.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c4a58ede1245/disk-e7aa5724.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c1d9b8392ed2/vmlinux-e7aa5724.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4ceeea28fcce/bzImage-e7aa5724.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c77c6c...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in mark_buffer_dirty_inode / mark_buffer_dirty_inode

write to 0xffff88812c76fd58 of 8 bytes by task 5176 on cpu 0:
mark_buffer_dirty_inode+0x18c/0x1c0 fs/buffer.c:693
fat_mirror_bhs+0x234/0x320 fs/fat/fatent.c:398
fat_alloc_clusters+0xb48/0xc50 fs/fat/fatent.c:543
fat_add_cluster fs/fat/inode.c:108 [inline]
__fat_get_block fs/fat/inode.c:155 [inline]
fat_get_block+0x258/0x5e0 fs/fat/inode.c:190
__block_write_begin_int+0x400/0xf90 fs/buffer.c:2145
block_write_begin fs/buffer.c:2256 [inline]
cont_write_begin+0x5fe/0x970 fs/buffer.c:2594
fat_write_begin+0x4f/0xe0 fs/fat/inode.c:230
generic_perform_write+0x183/0x490 mm/filemap.c:4314
__generic_file_write_iter+0x9e/0x120 mm/filemap.c:4431
generic_file_write_iter+0x8d/0x310 mm/filemap.c:4457
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5a6/0x9f0 fs/read_write.c:686
ksys_write+0xdc/0x1a0 fs/read_write.c:738
__do_sys_write fs/read_write.c:749 [inline]
__se_sys_write fs/read_write.c:746 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:746
x64_sys_call+0x2847/0x3000 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812c76fd58 of 8 bytes by task 5179 on cpu 1:
mark_buffer_dirty_inode+0x95/0x1c0 fs/buffer.c:689
fat_mirror_bhs+0x234/0x320 fs/fat/fatent.c:398
fat_alloc_clusters+0xb48/0xc50 fs/fat/fatent.c:543
fat_add_cluster fs/fat/inode.c:108 [inline]
__fat_get_block fs/fat/inode.c:155 [inline]
fat_get_block+0x258/0x5e0 fs/fat/inode.c:190
__block_write_begin_int+0x400/0xf90 fs/buffer.c:2145
block_write_begin fs/buffer.c:2256 [inline]
cont_write_begin+0x5fe/0x970 fs/buffer.c:2594
fat_write_begin+0x4f/0xe0 fs/fat/inode.c:230
generic_perform_write+0x183/0x490 mm/filemap.c:4314
__generic_file_write_iter+0x9e/0x120 mm/filemap.c:4431
generic_file_write_iter+0x8d/0x310 mm/filemap.c:4457
aio_write+0x2fe/0x430 fs/aio.c:1634
__io_submit_one fs/aio.c:-1 [inline]
io_submit_one+0xbc1/0x1350 fs/aio.c:2053
__do_sys_io_submit fs/aio.c:2112 [inline]
__se_sys_io_submit+0xfb/0x280 fs/aio.c:2082
__x64_sys_io_submit+0x43/0x50 fs/aio.c:2082
x64_sys_call+0x2e40/0x3000 arch/x86/include/generated/asm/syscalls_64.h:210
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000000000000 -> 0xffff88811a92a008

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5179 Comm: syz.4.7392 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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