[moderation] [fs?] KCSAN: data-race in drop_nlink / vfs_coredump

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 63804fed149a Linux 6.19-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15240322580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8e27f4588a0f2183
dashboard link: https://syzkaller.appspot.com/bug?extid=f09e3df5f66de2ecb09b
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [bra...@kernel.org ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a01803567280/disk-63804fed.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2e8f54c26352/vmlinux-63804fed.xz
kernel image: https://storage.googleapis.com/syzbot-assets/aedebc96acfe/bzImage-63804fed.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f09e3d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in drop_nlink / vfs_coredump

write to 0xffff888101601520 of 4 bytes by task 8062 on cpu 1:
drop_nlink+0x3d/0xa0 fs/inode.c:418
__simple_unlink fs/libfs.c:792 [inline]
simple_unlink+0x60/0x80 fs/libfs.c:806
shmem_unlink+0x12d/0x140 mm/shmem.c:3991
vfs_unlink+0x28b/0x440 fs/namei.c:5378
do_unlinkat+0x1e2/0x4b0 fs/namei.c:5448
coredump_file fs/coredump.c:902 [inline]
do_coredump fs/coredump.c:1099 [inline]
vfs_coredump+0x1553/0x3120 fs/coredump.c:1200
get_signal+0xd7b/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:41 [inline]
exit_to_user_mode_loop kernel/entry/common.c:75 [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+0xf7/0x510 kernel/entry/common.c:196
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

read to 0xffff888101601520 of 4 bytes by task 8061 on cpu 0:
coredump_file fs/coredump.c:937 [inline]
do_coredump fs/coredump.c:1099 [inline]
vfs_coredump+0x165f/0x3120 fs/coredump.c:1200
get_signal+0xd7b/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:41 [inline]
exit_to_user_mode_loop kernel/entry/common.c:75 [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+0xf7/0x510 kernel/entry/common.c:196
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: 8061 Comm: syz.0.1117 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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