KCSAN: data-race in d_make_discardable / dentry_kill

Status: moderation: reported on 2026/06/25 18:14
Subsystems: fs
Labels: race:benign prio:low
[Documentation on labels]
Reported-by: syzbot+d1d6dc20ca5d8eb0943c@syzkaller.appspotmail.com
First crash: 49d, last: 8d00h
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
92af6d00 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ KCSAN: data-race in d_make_discardable / dentry_kill 2026/06/27 00:00 2026/06/27 00:00 2026/06/27 00:50 7ff32d8b
393b68b8 assessment-kcsan Benign: ✅ KCSAN: data-race in d_make_discardable / dentry_kill 2026/06/25 18:14 2026/06/25 18:14 2026/06/25 18:34 7ff32d8b

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

write to 0xffff88811e1f4f00 of 4 bytes by task 3947 on cpu 1:
 d_make_discardable+0x4f/0x90 fs/dcache.c:1050
 simple_unlink+0x68/0x80 fs/libfs.c:808
 shmem_unlink+0x12d/0x140 mm/shmem.c:3927
 vfs_unlink+0x1c3/0x490 fs/namei.c:5515
 filename_unlinkat+0x1dc/0x410 fs/namei.c:5585
 __do_sys_unlink fs/namei.c:5620 [inline]
 __se_sys_unlink+0x2b/0xe0 fs/namei.c:5617
 __x64_sys_unlink+0x1f/0x30 fs/namei.c:5617
 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

read to 0xffff88811e1f4f00 of 4 bytes by task 5935 on cpu 0:
 dentry_unlist fs/dcache.c:694 [inline]
 dentry_kill+0x2d3/0x500 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:5588
 __do_sys_unlink fs/namei.c:5620 [inline]
 __se_sys_unlink+0x2b/0xe0 fs/namei.c:5617
 __x64_sys_unlink+0x1f/0x30 fs/namei.c:5617
 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: 0x08200080 -> 0x00000080

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 5935 Comm: udevd Tainted: G        W           syzkaller #0 PREEMPT(lazy) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
==================================================================
udevd[5935]: inotify_add_watch(7, /dev/loop2p4, 10) failed: No such file or directory

Crashes (13):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/06 16:42 upstream fcaeecb8b0cd c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/08/06 14:16 upstream 0d8395707651 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/27 11:24 upstream f5098b6bae76 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/26 02:48 upstream 0ce37745d4bf 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/23 20:45 upstream d326f83e819c 71a13572 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/23 11:58 upstream 4539944e5151 71a13572 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/22 23:22 upstream 4539944e5151 881ce5c2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/21 22:47 upstream 248951ddc14d b561ce9c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/18 05:19 upstream 94515f3a7d42 72524a66 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/08 08:47 upstream 0e35b9b6ec0f 88a4b44c .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/06 23:57 upstream 8cdeaa50eae8 8e71ce95 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/07/02 01:09 upstream 4a50a141f05a 27192279 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
2026/06/25 18:14 upstream a142da0b2d32 cfa969bf .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in d_make_discardable / dentry_kill
* Struck through repros no longer work on HEAD.