[moderation] [mm?] [fs?] KCSAN: data-race in __writeback_single_inode / xas_clear_mark (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 083fc6d7fa0d Merge tag 'sched-urgent-2025-09-26' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1596327c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c7f65ba98bb01573
dashboard link: https://syzkaller.appspot.com/bug?extid=68fb935b4a2bf2f83ce0
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ak...@linux-foundation.org linux-...@vger.kernel.org linux-...@vger.kernel.org linu...@kvack.org wi...@infradead.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c167ba38cbbe/disk-083fc6d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fd604c516d96/vmlinux-083fc6d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dcbbcb23e97f/bzImage-083fc6d7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+68fb93...@syzkaller.appspotmail.com

loop4: detected capacity change from 0 to 512
EXT4-fs: Ignoring removed mblk_io_submit option
EXT4-fs (loop4): encrypted files will use data=ordered instead of data journaling mode
EXT4-fs (loop4): 1 truncate cleaned up
==================================================================
BUG: KCSAN: data-race in __writeback_single_inode / xas_clear_mark

write to 0xffff88811a43b6ac of 4 bytes by task 13486 on cpu 0:
xa_mark_clear lib/xarray.c:77 [inline]
xas_clear_mark+0x16b/0x180 lib/xarray.c:932
__folio_start_writeback+0x2ce/0x440 mm/page-writeback.c:3088
ext4_bio_write_folio+0x5ad/0x9f0 fs/ext4/page-io.c:583
mpage_submit_folio fs/ext4/inode.c:2080 [inline]
mpage_process_page_bufs+0x4a1/0x620 fs/ext4/inode.c:2191
mpage_prepare_extent_to_map+0x786/0xc00 fs/ext4/inode.c:2736
ext4_do_writepages+0x708/0x2750 fs/ext4/inode.c:2877
ext4_writepages+0x176/0x300 fs/ext4/inode.c:3025
do_writepages+0x1c3/0x310 mm/page-writeback.c:2634
filemap_fdatawrite_wbc mm/filemap.c:386 [inline]
__filemap_fdatawrite_range mm/filemap.c:419 [inline]
file_write_and_wait_range+0x156/0x2c0 mm/filemap.c:794
generic_buffers_fsync_noflush+0x45/0x120 fs/buffer.c:609
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_dio_write_iter fs/ext4/file.c:613 [inline]
ext4_file_write_iter+0xdbf/0xf00 fs/ext4/file.c:721
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 0xffff88811a43b6ac of 4 bytes by task 13480 on cpu 1:
xa_marked include/linux/xarray.h:424 [inline]
mapping_tagged include/linux/fs.h:543 [inline]
__writeback_single_inode+0x1f9/0x7c0 fs/fs-writeback.c:1731
writeback_single_inode+0x167/0x3e0 fs/fs-writeback.c:1801
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_dio_write_iter fs/ext4/file.c:613 [inline]
ext4_file_write_iter+0xdbf/0xf00 fs/ext4/file.c:721
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: 0x0e000021 -> 0x04000021

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 13480 Comm: syz.4.2814 Not tainted syzkaller #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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