KCSAN: data-race in __d_instantiate / path_lookupat (2)

Status: moderation: reported C repro on 2026/06/23 17:59
Subsystems: fs
Labels: race:benign prio:low
[Documentation on labels]
Reported-by: syzbot+c900d69656aab3702986@syzkaller.appspotmail.com
First crash: 102d, last: 1h00m
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
d4007c08 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KCSAN: data-race in __d_instantiate / path_lookupat (2) 2026/06/25 00:01 2026/06/25 00:01 2026/06/25 00:38 2e5297c5
04bc1d99 assessment-kcsan Benign: ✅ ❓ KCSAN: data-race in __d_instantiate / path_lookupat (2) 2026/06/23 17:59 2026/06/23 17:59 2026/06/23 18:26 e30e5c89
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in __d_instantiate / path_lookupat fs 6 4 224d 293d 0/29 auto-obsoleted due to no activity on 2026/04/18 04:16

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

read-write to 0xffff8881004f23c0 of 4 bytes by task 3644 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:2158
 d_instantiate_new+0x68/0xf0 fs/dcache.c:2204
 ext4_add_nondir+0x187/0x1b0 fs/ext4/namei.c:2796
 ext4_symlink+0x58f/0x660 fs/ext4/namei.c:3435
 vfs_symlink+0xfd/0x220 fs/namei.c:5794
 filename_symlinkat+0xe8/0x2b0 fs/namei.c:5819
 __do_sys_symlink fs/namei.c:5846 [inline]
 __se_sys_symlink+0x42/0x1b0 fs/namei.c:5842
 __x64_sys_symlink+0x31/0x40 fs/namei.c:5842
 x64_sys_call+0x211f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:89
 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 0xffff8881004f23c0 of 4 bytes by task 3645 on cpu 1:
 d_managed include/linux/dcache.h:433 [inline]
 step_into fs/namei.c:2140 [inline]
 walk_component fs/namei.c:2288 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x19b/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: 0x00040040 -> 0x00340040

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3645 Comm: syz-executor101 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
==================================================================
==================================================================
BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff88810061c600 of 4 bytes by task 3644 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:2158
 d_instantiate_new+0x68/0xf0 fs/dcache.c:2204
 ext4_add_nondir+0x187/0x1b0 fs/ext4/namei.c:2796
 ext4_symlink+0x58f/0x660 fs/ext4/namei.c:3435
 vfs_symlink+0xfd/0x220 fs/namei.c:5794
 filename_symlinkat+0xe8/0x2b0 fs/namei.c:5819
 __do_sys_symlink fs/namei.c:5846 [inline]
 __se_sys_symlink+0x42/0x1b0 fs/namei.c:5842
 __x64_sys_symlink+0x31/0x40 fs/namei.c:5842
 x64_sys_call+0x211f/0x2550 arch/x86/include/generated/asm/syscalls_64.h:89
 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 0xffff88810061c600 of 4 bytes by task 3645 on cpu 1:
 d_revalidate fs/namei.c:1034 [inline]
 lookup_fast+0xf1/0x320 fs/namei.c:1868
 walk_component fs/namei.c:2278 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x120/0x4c0 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: 0x00040040 -> 0x00340040

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3645 Comm: syz-executor101 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
==================================================================
==================================================================
BUG: KCSAN: data-race in dont_mount / path_lookupat

read-write to 0xffff888105d61000 of 4 bytes by task 3644 on cpu 0:
 dont_mount+0x2a/0x40 include/linux/dcache.h:412
 vfs_unlink+0x202/0x490 fs/namei.c:5651
 filename_unlinkat+0x1dc/0x410 fs/namei.c:5719
 __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 0xffff888105d61000 of 4 bytes by task 3645 on cpu 1:
 d_managed include/linux/dcache.h:433 [inline]
 step_into fs/namei.c:2140 [inline]
 walk_component fs/namei.c:2288 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x19b/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: 0x00340040 -> 0x00040040

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3645 Comm: syz-executor101 Not tainted syzkaller #0 PREEMPT(lazy) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
==================================================================

Crashes (7):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/04 00:59 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git a74306e2e676 680aa3e1 .config console log report C ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/10/01 07:16 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 551c722f4080 a3c7249d .config console log report C ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/09/06 01:31 upstream 0d9ff90a5422 4f7b22a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/08/15 05:27 upstream dac3e89a2c90 746171ee .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/08/05 11:50 upstream c21bb4193868 52aa2820 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/08/01 10:00 upstream 0131b508c0e2 e611ffe1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
2026/06/23 17:59 upstream 502d801f0ab0 4b1d8f01 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in __d_instantiate / path_lookupat
* Struck through repros no longer work on HEAD.