syzbot


KCSAN: data-race in drop_nlink / vfs_coredump

Status: moderation: reported on 2026/01/26 21:05
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+f09e3df5f66de2ecb09b@syzkaller.appspotmail.com
First crash: 50d, last: 19h32m
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
036f8d23-b023-408e-9165-e6b193fabd7f assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in drop_nlink / vfs_coredump 2026/01/26 23:22 2026/01/26 23:22 2026/01/26 23:24 efb3e894dd7e30475c92970989c58e5aad3d5e7b

Sample crash report:
==================================================================
BUG: KCSAN: data-race in drop_nlink / vfs_coredump

write to 0xffff88811b612690 of 4 bytes by task 4734 on cpu 1:
 drop_nlink+0x3d/0xa0 fs/inode.c:419
 __simple_unlink fs/libfs.c:794 [inline]
 simple_unlink+0x60/0x80 fs/libfs.c:808
 shmem_unlink+0x12d/0x140 mm/shmem.c:4005
 vfs_unlink+0x1c7/0x490 fs/namei.c:5470
 filename_unlinkat+0x1e2/0x410 fs/namei.c:5540
 coredump_file fs/coredump.c:903 [inline]
 do_coredump fs/coredump.c:1100 [inline]
 vfs_coredump+0x1556/0x3130 fs/coredump.c:1201
 get_signal+0xd80/0xf60 kernel/signal.c:3019
 arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:98 [inline]
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:270 [inline]
 irqentry_exit_to_user_mode include/linux/irq-entry-common.h:339 [inline]
 irqentry_exit+0xf7/0x520 kernel/entry/common.c:219
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

read to 0xffff88811b612690 of 4 bytes by task 4735 on cpu 0:
 coredump_file fs/coredump.c:938 [inline]
 do_coredump fs/coredump.c:1100 [inline]
 vfs_coredump+0x166a/0x3130 fs/coredump.c:1201
 get_signal+0xd80/0xf60 kernel/signal.c:3019
 arch_do_signal_or_restart+0x96/0x450 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:98 [inline]
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 irqentry_exit_to_user_mode_prepare include/linux/irq-entry-common.h:270 [inline]
 irqentry_exit_to_user_mode include/linux/irq-entry-common.h:339 [inline]
 irqentry_exit+0xf7/0x520 kernel/entry/common.c:219
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

value changed: 0x00000001 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 4735 Comm: syz.6.326 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/17 14:05 upstream 2d1373e4246d c01bca74 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in drop_nlink / vfs_coredump
2026/01/26 21:04 upstream 63804fed149a a4c52dd6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in drop_nlink / vfs_coredump
* Struck through repros no longer work on HEAD.