[moderation] [ext4?] KCSAN: data-race in __mark_inode_dirty / generic_buffers_fsync_noflush (4)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 1896ce8eb6c6 Merge tag 'fsverity-for-linus' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1332a6e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6dc7116781ce86d1
dashboard link: https://syzkaller.appspot.com/bug?extid=052881ffc82df6662cb0
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/6f2a5c5dc53e/disk-1896ce8e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3f3885b31c84/vmlinux-1896ce8e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/96c843387fea/bzImage-1896ce8e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+052881...@syzkaller.appspotmail.com

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

write to 0xffff88811a0c0ea8 of 4 bytes by task 8388 on cpu 1:
__mark_inode_dirty+0x248/0x750 fs/fs-writeback.c:2597
ext4_mb_new_blocks+0x10b9/0x2080 fs/ext4/mballoc.c:-1
ext4_alloc_branch fs/ext4/indirect.c:340 [inline]
ext4_ind_map_blocks+0xb86/0x14f0 fs/ext4/indirect.c:635
ext4_map_create_blocks fs/ext4/inode.c:611 [inline]
ext4_map_blocks+0x598/0xd00 fs/ext4/inode.c:811
_ext4_get_block+0x10a/0x350 fs/ext4/inode.c:910
ext4_get_block+0x39/0x50 fs/ext4/inode.c:927
ext4_block_write_begin+0x5e5/0xc00 fs/ext4/inode.c:1198
ext4_write_begin+0x647/0xeb0 fs/ext4/ext4_jbd2.h:-1
generic_perform_write+0x184/0x490 mm/filemap.c:4175
ext4_buffered_write_iter+0x1ee/0x3c0 fs/ext4/file.c:299
ext4_dio_write_iter fs/ext4/file.c:613 [inline]
ext4_file_write_iter+0xdbf/0xf00 fs/ext4/file.c:721
iter_file_splice_write+0x663/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x153/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x30f/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 0xffff88811a0c0ea8 of 4 bytes by task 8395 on cpu 0:
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+0x10d/0x130 fs/sync.c:187
generic_write_sync include/linux/fs.h:3036 [inline]
ext4_buffered_write_iter+0x34f/0x3c0 fs/ext4/file.c:305
ext4_dio_write_iter fs/ext4/file.c:613 [inline]
ext4_file_write_iter+0xdbf/0xf00 fs/ext4/file.c:721
iter_file_splice_write+0x663/0xa60 fs/splice.c:738
do_splice_from fs/splice.c:938 [inline]
direct_splice_actor+0x153/0x2a0 fs/splice.c:1161
splice_direct_to_actor+0x30f/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: 0x00000040 -> 0x00000070

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 8395 Comm: syz.0.2121 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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