syzbot


KCSAN: data-race in __d_instantiate / lookup_fast (12)

Status: moderation: reported on 2026/01/18 23:39
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+1db8e7bac42204b93ef4@syzkaller.appspotmail.com
First crash: 21d, last: 4d11h
Similar bugs (11)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_instantiate / lookup_fast (6) ext4 6 53 637d 793d 0/29 auto-obsoleted due to no activity on 2024/06/16 23:52
upstream KCSAN: data-race in __d_instantiate / lookup_fast ext4 6 6 2115d 2239d 0/29 auto-closed as invalid on 2020/06/18 13:33
upstream KCSAN: data-race in __d_instantiate / lookup_fast (4) ext4 6 16 1282d 1398d 0/29 auto-closed as invalid on 2022/09/10 18:37
upstream KCSAN: data-race in __d_instantiate / lookup_fast (5) ext4 6 7 1191d 1243d 0/29 auto-obsoleted due to no activity on 2022/12/11 12:03
upstream KCSAN: data-race in __d_instantiate / lookup_fast (2) fs 6 1 1824d 1824d 0/29 auto-closed as invalid on 2021/03/18 02:49
upstream KCSAN: data-race in __d_instantiate / lookup_fast (3) ext4 6 1 1671d 1671d 0/29 auto-closed as invalid on 2021/08/17 22:04
upstream KCSAN: data-race in __d_instantiate / lookup_fast (10) fs 6 1 256d 256d 0/29 auto-obsoleted due to no activity on 2025/07/24 00:58
upstream KCSAN: data-race in __d_instantiate / lookup_fast (8) fs 6 1 490d 490d 0/29 auto-obsoleted due to no activity on 2024/11/11 02:07
upstream KCSAN: data-race in __d_instantiate / lookup_fast (9) fs 6 1 399d 399d 0/29 auto-obsoleted due to no activity on 2025/03/03 11:43
upstream KCSAN: data-race in __d_instantiate / lookup_fast (7) ext4 6 1 599d 599d 0/29 auto-obsoleted due to no activity on 2024/07/25 04:38
upstream KCSAN: data-race in __d_instantiate / lookup_fast (11) fs 6 1 163d 163d 0/29 auto-obsoleted due to no activity on 2025/10/24 20:01

Sample crash report:
==================================================================
BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff888107ba4780 of 4 bytes by task 3307 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:1987
 d_make_persistent+0x78/0x110 fs/dcache.c:2803
 shmem_mknod+0x15f/0x170 mm/shmem.c:3915
 shmem_mkdir+0x33/0x70 mm/shmem.c:3956
 vfs_mkdir+0x510/0x560 fs/namei.c:5139
 do_mkdirat+0x133/0x3b0 fs/namei.c:5173
 __do_sys_mkdir fs/namei.c:5200 [inline]
 __se_sys_mkdir fs/namei.c:5198 [inline]
 __x64_sys_mkdir+0x42/0x50 fs/namei.c:5198
 x64_sys_call+0x2f32/0x3000 arch/x86/include/generated/asm/syscalls_64.h:84
 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 0xffff888107ba4780 of 4 bytes by task 3306 on cpu 1:
 d_revalidate fs/namei.c:976 [inline]
 lookup_fast+0xf0/0x320 fs/namei.c:1814
 walk_component fs/namei.c:2225 [inline]
 lookup_last fs/namei.c:2730 [inline]
 path_lookupat+0x15c/0x500 fs/namei.c:2754
 filename_lookup+0x190/0x390 fs/namei.c:2783
 vfs_statx+0x96/0x170 fs/stat.c:353
 vfs_fstatat+0x115/0x170 fs/stat.c:375
 __do_sys_newfstatat fs/stat.c:542 [inline]
 __se_sys_newfstatat+0x55/0x3e0 fs/stat.c:536
 __x64_sys_newfstatat+0x55/0x70 fs/stat.c:536
 x64_sys_call+0x111f/0x3000 arch/x86/include/generated/asm/syscalls_64.h:263
 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: 0x00000080 -> 0x08100080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3306 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================
udevd[3306]: inotify_add_watch(7, /dev/loop2p3, 10) failed: No such file or directory

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/05 02:49 upstream 5fd0a1df5d05 ea10c935 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / lookup_fast
2026/01/18 23:38 upstream e84d960149e7 20d37d28 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / lookup_fast
* Struck through repros no longer work on HEAD.