[moderation] [exfat?] KCSAN: data-race in mark_buffer_dirty_inode / sync_mapping_buffers (11)

Hello,

syzbot found the following issue on:

HEAD commit: b1427432d3b6 Merge tag 'iommu-fixes-v6.15-rc7' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10dc28e8580000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea93cce608593e25
dashboard link: https://syzkaller.appspot.com/bug?extid=090227ea7a5578fc6b9c
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [[email protected] [email protected] [email protected] [email protected] [email protected]]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/54611480ec17/disk-b1427432.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6343d2d2eb84/vmlinux-b1427432.xz
kernel image: https://storage.googleapis.com/syzbot-assets/51ac8320af33/bzImage-b1427432.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

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

write to 0xffff888106fca330 of 8 bytes by task 10294 on cpu 0:
__remove_assoc_queue fs/buffer.c:523 [inline]
fsync_buffers_list fs/buffer.c:796 [inline]
sync_mapping_buffers+0x163/0x7d0 fs/buffer.c:584
fat_file_fsync+0xaa/0x100 fs/fat/file.c:195
vfs_fsync_range+0x10a/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:2976 [inline]
generic_file_write_iter+0x1b8/0x2f0 mm/filemap.c:4250
iter_file_splice_write+0x5ef/0x970 fs/splice.c:738
do_splice_from fs/splice.c:935 [inline]
direct_splice_actor+0x153/0x2a0 fs/splice.c:1158
splice_direct_to_actor+0x30f/0x680 fs/splice.c:1102
do_splice_direct_actor fs/splice.c:1201 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1227
do_sendfile+0x380/0x640 fs/read_write.c:1368
__do_sys_sendfile64 fs/read_write.c:1429 [inline]
__se_sys_sendfile64 fs/read_write.c:1415 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1415
x64_sys_call+0xb39/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888106fca330 of 8 bytes by task 10301 on cpu 1:
mark_buffer_dirty_inode+0x95/0x1c0 fs/buffer.c:689
fat32_ent_put+0x73/0x90 fs/fat/fatent.c:192
fat_ent_write+0x69/0xe0 fs/fat/fatent.c:417
fat_chain_add+0x15b/0x3f0 fs/fat/misc.c:136
fat_add_cluster fs/fat/inode.c:112 [inline]
__fat_get_block fs/fat/inode.c:154 [inline]
fat_get_block+0x46c/0x5e0 fs/fat/inode.c:189
__block_write_begin_int+0x41c/0xf70 fs/buffer.c:2151
block_write_begin fs/buffer.c:2262 [inline]
cont_write_begin+0x5a3/0x8e0 fs/buffer.c:2601
fat_write_begin+0x4f/0xe0 fs/fat/inode.c:228
generic_perform_write+0x181/0x490 mm/filemap.c:4103
__generic_file_write_iter+0x9e/0x120 mm/filemap.c:4220
generic_file_write_iter+0x8d/0x2f0 mm/filemap.c:4246
new_sync_write fs/read_write.c:591 [inline]
vfs_write+0x4a0/0x8d0 fs/read_write.c:684
ksys_write+0xda/0x1a0 fs/read_write.c:736
__do_sys_write fs/read_write.c:747 [inline]
__se_sys_write fs/read_write.c:744 [inline]
__x64_sys_write+0x40/0x50 fs/read_write.c:744
x64_sys_call+0x2cdd/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:2
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd0/0x1a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888106db7508 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10301 Comm: syz.6.2145 Not tainted 6.15.0-rc7-syzkaller-00144-gb1427432d3b6 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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