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KCSAN: data-race in __d_instantiate / lookup_fast (13)

Status: moderation: reported on 2026/05/29 11:02
Subsystems: fs
Labels: race:benign prio:low
[Documentation on labels]
Reported-by: syzbot+54b3bbfb896275f5fb03@syzkaller.appspotmail.com
First crash: 14d, last: 14d
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
288ec6c1-ef80-46e6-a38a-3785892e6b95 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KCSAN: data-race in __d_instantiate / lookup_fast (13) 2026/06/02 18:44 2026/06/02 18:44 2026/06/02 19:44 62fe15281f5011cd203d8845b8767b10e7443aa5
cdeb93ea-8c73-462f-98a8-0356d89f7eb9 assessment-kcsan Benign: ✅ ❓ KCSAN: data-race in __d_instantiate / lookup_fast (13) 2026/05/29 21:33 2026/05/29 21:33 2026/05/29 22:01 6b4a844333e83556da95d61d7f207e7ef5cd4bc6
▶ ▼ Similar bugs (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_instantiate / lookup_fast (12) fs 6 4 107d 145d 0/29 auto-obsoleted due to no activity on 2026/04/22 20:55
upstream KCSAN: data-race in __d_instantiate / lookup_fast (6) ext4 6 53 761d 917d 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 2238d 2363d 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 1406d 1521d 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 1314d 1367d 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 1948d 1948d 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 1795d 1795d 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 380d 380d 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 614d 614d 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 522d 522d 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 723d 722d 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 287d 287d 0/29 auto-obsoleted due to no activity on 2025/10/24 20:01

Sample crash report:
capability: warning: `syz.0.159' uses deprecated v2 capabilities in a way that may be insecure
==================================================================
BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff888106c62480 of 4 bytes by task 4160 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:2054
 d_make_persistent+0x72/0x110 fs/dcache.c:2870
 shmem_mknod+0x15f/0x170 mm/shmem.c:3881
 shmem_create+0x34/0x50 mm/shmem.c:3933
 lookup_open fs/namei.c:4511 [inline]
 open_last_lookups fs/namei.c:4611 [inline]
 path_openat+0xd75/0x2050 fs/namei.c:4855
 do_file_open+0x16c/0x290 fs/namei.c:4887
 do_sys_openat2+0x94/0x130 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1381
 x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888106c62480 of 4 bytes by task 4159 on cpu 1:
 d_revalidate fs/namei.c:1029 [inline]
 lookup_fast+0xf0/0x320 fs/namei.c:1863
 lookup_fast_for_open fs/namei.c:4548 [inline]
 open_last_lookups fs/namei.c:4582 [inline]
 path_openat+0x436/0x2050 fs/namei.c:4855
 do_file_open+0x16c/0x290 fs/namei.c:4887
 do_sys_openat2+0x94/0x130 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1381
 x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000080 -> 0x08200080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 4159 Comm: syz.0.159 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/29 11:01 upstream 8fde5d1d47f6 4624854e .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.