KCSAN: data-race in dentry_kill / step_into_slowpath

Status: moderation: reported on 2026/09/28 02:11
Subsystems: fs
Labels: race:benign
[Documentation on labels]
Reported-by: syzbot+c389f0c1b3feb6d5a33a@syzkaller.appspotmail.com
First crash: 8h03m, last: 8h03m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
feced9a7 assessment-kcsan Benign: ✅ ❓ KCSAN: data-race in dentry_kill / step_into_slowpath 2026/09/28 02:29 2026/09/28 02:29 2026/09/28 03:32 a3c7249d

Sample crash report:
==================================================================
BUG: KCSAN: data-race in dentry_kill / step_into_slowpath

read-write to 0xffff8881073c8c00 of 4 bytes by task 3288 on cpu 0:
 dentry_unlist fs/dcache.c:664 [inline]
 dentry_kill+0x22b/0x500 fs/dcache.c:840
 finish_dput+0x16/0x1d0 fs/dcache.c:1001
 dput+0x48/0x50 fs/dcache.c:1042
 end_dirop fs/namei.c:2956 [inline]
 filename_unlinkat+0x217/0x410 fs/namei.c:5722
 __do_sys_unlink fs/namei.c:5754 [inline]
 __se_sys_unlink+0x2b/0xe0 fs/namei.c:5751
 __x64_sys_unlink+0x1f/0x30 fs/namei.c:5751
 x64_sys_call+0x18ee/0x2550 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881073c8c00 of 4 bytes by task 2984 on cpu 1:
 d_managed include/linux/dcache.h:433 [inline]
 handle_mounts fs/namei.c:1738 [inline]
 step_into_slowpath+0xea/0x4c0 fs/namei.c:2104
 step_into fs/namei.c:2152 [inline]
 walk_component fs/namei.c:2288 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x2eb/0x4c0 fs/namei.c:2813
 filename_lookup+0x18f/0x390 fs/namei.c:2842
 do_readlinkat+0x74/0x2f0 fs/stat.c:571
 __do_sys_readlink fs/stat.c:605 [inline]
 __se_sys_readlink fs/stat.c:602 [inline]
 __x64_sys_readlink+0x47/0x60 fs/stat.c:602
 x64_sys_call+0x1d41/0x2550 arch/x86/include/generated/asm/syscalls_64.h:90
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x112/0x360 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00300080 -> 0x00004080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2984 Comm: udevd Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/28 02:10 upstream efb44d93a620 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in dentry_kill / step_into_slowpath
* Struck through repros no longer work on HEAD.