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KCSAN: data-race in __d_drop / fast_dput (3)

Status: moderation: reported on 2026/01/26 07:47
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+88b1b158ab29280f07a2@syzkaller.appspotmail.com
First crash: 10d, last: 11h02m
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_drop / fast_dput (2) fs 6 3 1596d 1605d 0/29 auto-closed as invalid on 2021/10/28 07:38
upstream KCSAN: data-race in __d_drop / fast_dput fs 6 1 1679d 1679d 0/29 auto-closed as invalid on 2021/08/06 11:24

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

write to 0xffff88811b040b50 of 8 bytes by task 2999 on cpu 1:
 __d_drop+0x14d/0x240 fs/dcache.c:576
 __dentry_kill+0x122/0x460 fs/dcache.c:668
 finish_dput+0x2b/0x200 fs/dcache.c:879
 dput+0x52/0x60 fs/dcache.c:928
 lookup_one_qstr_excl+0x15a/0x250 fs/namei.c:-1
 __start_dirop fs/namei.c:2875 [inline]
 start_dirop fs/namei.c:2884 [inline]
 do_unlinkat+0x149/0x4b0 fs/namei.c:5429
 __do_sys_unlink fs/namei.c:5483 [inline]
 __se_sys_unlink fs/namei.c:5481 [inline]
 __x64_sys_unlink+0x2e/0x40 fs/namei.c:5481
 x64_sys_call+0x2f48/0x3000 arch/x86/include/generated/asm/syscalls_64.h:88
 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 0xffff88811b040b50 of 8 bytes by task 3750 on cpu 0:
 hlist_bl_unhashed include/linux/list_bl.h:54 [inline]
 d_unhashed include/linux/dcache.h:366 [inline]
 retain_dentry fs/dcache.c:753 [inline]
 fast_dput+0x5f/0x2c0 fs/dcache.c:849
 dput+0x24/0x60 fs/dcache.c:924
 end_dirop fs/namei.c:2898 [inline]
 do_unlinkat+0x217/0x4b0 fs/namei.c:5451
 __do_sys_unlink fs/namei.c:5483 [inline]
 __se_sys_unlink fs/namei.c:5481 [inline]
 __x64_sys_unlink+0x2e/0x40 fs/namei.c:5481
 x64_sys_call+0x2f48/0x3000 arch/x86/include/generated/asm/syscalls_64.h:88
 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: 0xffff8882377458b0 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3750 Comm: udevd Not tainted syzkaller #0 PREEMPT(voluntary) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================

Crashes (20):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/05 03:55 upstream f14faaf3a1fb ea10c935 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/04 15:12 upstream 5fd0a1df5d05 ea10c935 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/04 12:04 upstream 5fd0a1df5d05 42b01fab .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/03 23:01 upstream de0674d9bc69 42b01fab .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/03 12:08 upstream 6bd9ed02871f 6df4c87a .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/02 22:49 upstream dee65f79364c d78927dd .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/01 21:28 upstream 9f2693489ef8 6b8752f2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/02/01 02:08 upstream ad9a728a3388 6b8752f2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/31 15:23 upstream ad9a728a3388 afc0c4d4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/31 09:56 upstream 283073725700 c75a2f6e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/30 19:41 upstream 4d310797262f ae7dc18c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/30 09:54 upstream 4d310797262f bfa73b7b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/30 00:59 upstream 8dfce8991b95 bfa73b7b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/29 19:20 upstream 8dfce8991b95 aeb6fdd5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/29 04:36 upstream 8dfce8991b95 0adc945e .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/28 04:08 upstream 1f97d9dcf536 3029c699 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/27 11:02 upstream fcb70a56f4d8 9a514c2f .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/27 06:46 upstream fcb70a56f4d8 efb3e894 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/26 13:59 upstream 63804fed149a a4c52dd6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
2026/01/26 07:46 upstream 023777797472 55756628 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_drop / fast_dput
* Struck through repros no longer work on HEAD.