[moderation] [ext4?] KCSAN: data-race in generic_buffers_fsync_noflush / inode_cgwb_move_to_attached (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fec734e8d564 Merge tag 'riscv-for-linus-v6.17-rc8' of git:..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16b282e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c7f65ba98bb01573
dashboard link: https://syzkaller.appspot.com/bug?extid=408c1ec498d73d48215a
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/348f9b61a4be/disk-fec734e8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a7739fb95415/vmlinux-fec734e8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b22b307d0d69/bzImage-fec734e8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+408c1e...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_buffers_fsync_noflush / inode_cgwb_move_to_attached

write to 0xffff888119c91300 of 4 bytes by task 6049 on cpu 0:
inode_cgwb_move_to_attached+0x9b/0x310 fs/fs-writeback.c:309
writeback_single_inode+0x2af/0x3e0 fs/fs-writeback.c:1818
sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2884
generic_buffers_fsync_noflush+0xd9/0x120 fs/buffer.c:619
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
vfs_fsync_range+0x10a/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3043 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
iter_file_splice_write+0x666/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2bb0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119c91300 of 4 bytes by task 6058 on cpu 1:
generic_buffers_fsync_noflush+0x80/0x120 fs/buffer.c:614
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
vfs_fsync_range+0x10a/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3043 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
iter_file_splice_write+0x666/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2bb0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000002 -> 0x00000020

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 6058 Comm: syz.0.1011 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================
==================================================================
BUG: KCSAN: data-race in generic_buffers_fsync_noflush / writeback_single_inode

write to 0xffff888119c91300 of 4 bytes by task 6049 on cpu 0:
writeback_single_inode+0x14a/0x3e0 fs/fs-writeback.c:1798
sync_inode_metadata+0x5b/0x90 fs/fs-writeback.c:2884
generic_buffers_fsync_noflush+0xd9/0x120 fs/buffer.c:619
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
vfs_fsync_range+0x10a/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3043 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
iter_file_splice_write+0x666/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2bb0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888119c91300 of 4 bytes by task 6058 on cpu 1:
generic_buffers_fsync_noflush+0x80/0x120 fs/buffer.c:614
ext4_fsync_nojournal fs/ext4/fsync.c:88 [inline]
ext4_sync_file+0x1ab/0x690 fs/ext4/fsync.c:147
vfs_fsync_range+0x10a/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3043 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_file_write_iter+0x383/0xf00 fs/ext4/file.c:-1
iter_file_splice_write+0x666/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x156/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x312/0x680 fs/splice.c:1105
do_splice_direct_actor fs/splice.c:1204 [inline]
do_splice_direct+0xda/0x150 fs/splice.c:1230
do_sendfile+0x380/0x650 fs/read_write.c:1370
__do_sys_sendfile64 fs/read_write.c:1431 [inline]
__se_sys_sendfile64 fs/read_write.c:1417 [inline]
__x64_sys_sendfile64+0x105/0x150 fs/read_write.c:1417
x64_sys_call+0x2bb0/0x2ff0 arch/x86/include/generated/asm/syscalls_64.h:41
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000020 -> 0x00000038

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 6058 Comm: syz.0.1011 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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