[moderation] [fs?] KCSAN: data-race in __fsnotify_parent / d_make_discardable

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b71e635feefc Merge tag 'cgroup-for-6.19-rc5-fixes' of git:..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15fc599a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c160236e1ef1e401
dashboard link: https://syzkaller.appspot.com/bug?extid=be42b00654c9742a4791
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [amir...@gmail.com ja...@suse.cz linux-...@vger.kernel.org linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/03aef7ad2d3e/disk-b71e635f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/39d65d4c2244/vmlinux-b71e635f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ba2913ff6bfa/bzImage-b71e635f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+be42b0...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __fsnotify_parent / d_make_discardable

write to 0xffff888107a5e840 of 4 bytes by task 3504 on cpu 0:
d_make_discardable+0x4f/0xa0 fs/dcache.c:936
simple_unlink+0x68/0x80 fs/libfs.c:807
shmem_unlink+0x12d/0x140 mm/shmem.c:3991
shmem_rename2+0x18e/0x310 mm/shmem.c:4072
vfs_rename+0x97f/0xad0 fs/namei.c:5938
do_renameat2+0x383/0x810 fs/namei.c:6056
__do_sys_rename fs/namei.c:6099 [inline]
__se_sys_rename fs/namei.c:6097 [inline]
__x64_sys_rename+0x58/0x70 fs/namei.c:6097
x64_sys_call+0x24e/0x3000 arch/x86/include/generated/asm/syscalls_64.h:83
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888107a5e840 of 4 bytes by task 3004 on cpu 1:
__fsnotify_parent+0xbc/0x3a0 fs/notify/fsnotify.c:245
fsnotify_parent include/linux/fsnotify.h:96 [inline]
fsnotify_path include/linux/fsnotify.h:113 [inline]
fsnotify_file include/linux/fsnotify.h:127 [inline]
fsnotify_open include/linux/fsnotify.h:446 [inline]
vfs_open+0x19c/0x1e0 fs/open.c:1101
do_open fs/namei.c:4637 [inline]
path_openat+0x1ddd/0x23b0 fs/namei.c:4796
do_filp_open+0x109/0x230 fs/namei.c:4823
do_sys_openat2+0xa6/0x150 fs/open.c:1430
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0xf2/0x120 fs/open.c:1447
x64_sys_call+0x2b07/0x3000 arch/x86/include/generated/asm/syscalls_64.h:258
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xca/0x2b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x08200080 -> 0x00200180

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 3004 Comm: udevd 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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