[moderation] [mm?] KCSAN: data-race in generic_fillattr / shmem_symlink (5)

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Oct 13, 2025, 6:26:26 PM (12 hours ago) Oct 13
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Hello,

syzbot found the following issue on:

HEAD commit: 3a8660878839 Linux 6.18-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1524467c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bafeb347352dd60e
dashboard link: https://syzkaller.appspot.com/bug?extid=2d0e5d2b4dbae91dc4fe
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [ak...@linux-foundation.org baoli...@linux.alibaba.com hu...@google.com linux-...@vger.kernel.org linu...@kvack.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/716425d8a25c/disk-3a866087.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7ef133e1ca3c/vmlinux-3a866087.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ef381199ff0e/bzImage-3a866087.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d0e5d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in generic_fillattr / shmem_symlink

write to 0xffff8881090df818 of 8 bytes by task 3493 on cpu 1:
inode_set_mtime_to_ts include/linux/fs.h:1838 [inline]
shmem_symlink+0x37a/0x3d0 mm/shmem.c:4131
vfs_symlink+0xd4/0x1e0 fs/namei.c:4817
do_symlinkat+0xc7/0x3c0 fs/namei.c:4843
__do_sys_symlink fs/namei.c:4864 [inline]
__se_sys_symlink fs/namei.c:4862 [inline]
__x64_sys_symlink+0x50/0x60 fs/namei.c:4862
x64_sys_call+0x23d0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:89
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff8881090df818 of 8 bytes by task 3304 on cpu 0:
inode_get_mtime_sec include/linux/fs.h:1820 [inline]
inode_get_mtime include/linux/fs.h:1830 [inline]
generic_fillattr+0x201/0x340 fs/stat.c:102
shmem_getattr+0x181/0x200 mm/shmem.c:1257
vfs_getattr_nosec+0x146/0x1e0 fs/stat.c:213
vfs_getattr fs/stat.c:262 [inline]
vfs_statx_path fs/stat.c:299 [inline]
vfs_statx+0x113/0x390 fs/stat.c:356
vfs_fstatat+0x115/0x170 fs/stat.c:375
__do_sys_newfstatat fs/stat.c:542 [inline]
__se_sys_newfstatat+0x55/0x260 fs/stat.c:536
__x64_sys_newfstatat+0x55/0x70 fs/stat.c:536
x64_sys_call+0x135a/0x3000 arch/x86/include/generated/asm/syscalls_64.h:263
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x0000000068ed7c73 -> 0x0000000068ed7c75

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3304 Comm: udevd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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