syzbot


KCSAN: data-race in dentry_kill / fast_dput

Status: moderation: reported on 2026/06/15 07:26
Subsystems: fs
Labels: race:benign
[Documentation on labels]
Reported-by: syzbot+1cfd29c242c7cd26da02@syzkaller.appspotmail.com
First crash: 3h00m, last: 3h00m
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
f6fc981a-7b9d-4261-a41c-11ca830ae798 assessment-kcsan Benign: ✅ KCSAN: data-race in dentry_kill / fast_dput 2026/06/15 07:26 2026/06/15 07:26 2026/06/15 07:51 4f06757f683a802254a4c8edbfe67ff801904c5e

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

write to 0xffff88811bf91e50 of 8 bytes by task 2982 on cpu 1:
 __d_drop fs/dcache.c:578 [inline]
 dentry_kill+0x139/0x500 fs/dcache.c:824
 finish_dput+0x16/0x1d0 fs/dcache.c:1001
 dput+0x48/0x50 fs/dcache.c:1042
 handle_mounts fs/namei.c:1753 [inline]
 step_into_slowpath+0x38c/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+0x329/0x390 fs/namei.c:2844
 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+0x2b51/0x3020 arch/x86/include/generated/asm/syscalls_64.h:90
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811bf91e50 of 8 bytes by task 18264 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:396 [inline]
 retain_dentry fs/dcache.c:872 [inline]
 fast_dput+0x64/0x2e0 fs/dcache.c:971
 dput+0x1f/0x50 fs/dcache.c:1040
 end_dirop fs/namei.c:2956 [inline]
 filename_unlinkat+0x217/0x410 fs/namei.c:5584
 __do_sys_unlink fs/namei.c:5616 [inline]
 __se_sys_unlink+0x2b/0xe0 fs/namei.c:5613
 __x64_sys_unlink+0x1f/0x30 fs/namei.c:5613
 x64_sys_call+0x2eb6/0x3020 arch/x86/include/generated/asm/syscalls_64.h:88
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x136/0x3c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff8882377e6140 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 18264 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/15 07:26 upstream 95e56f0f293e 1d2f3589 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in dentry_kill / fast_dput
* Struck through repros no longer work on HEAD.