syzbot

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BUG: KCSAN: data-race in set_nlink / set_nlink

read to 0xffff88810792c518 of 4 bytes by task 3000 on cpu 1:
 set_nlink+0x29/0xb0 fs/inode.c:-1
 kernfs_refresh_inode fs/kernfs/inode.c:182 [inline]
 kernfs_iop_permission+0x1e2/0x220 fs/kernfs/inode.c:290
 do_inode_permission fs/namei.c:578 [inline]
 inode_permission+0x31f/0x3b0 fs/namei.c:648
 lookup_inode_permission_may_exec fs/namei.c:688 [inline]
 may_lookup fs/namei.c:1958 [inline]
 link_path_walk+0x779/0xe30 fs/namei.c:2601
 path_lookupat+0x8c/0x500 fs/namei.c:2809
 filename_lookup+0x190/0x390 fs/namei.c:2839
 vfs_statx+0x96/0x170 fs/stat.c:353
 vfs_fstatat+0x118/0x170 fs/stat.c:373
 __do_sys_newfstatat fs/stat.c:538 [inline]
 __se_sys_newfstatat+0x55/0x3e0 fs/stat.c:532
 __x64_sys_newfstatat+0x55/0x70 fs/stat.c:532
 x64_sys_call+0x2c64/0x3020 arch/x86/include/generated/asm/syscalls_64.h:263
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

write to 0xffff88810792c518 of 4 bytes by task 3300 on cpu 0:
 set_nlink+0x99/0xb0 fs/inode.c:459
 kernfs_refresh_inode fs/kernfs/inode.c:182 [inline]
 kernfs_iop_permission+0x1e2/0x220 fs/kernfs/inode.c:290
 do_inode_permission fs/namei.c:578 [inline]
 inode_permission+0x31f/0x3b0 fs/namei.c:648
 lookup_inode_permission_may_exec fs/namei.c:688 [inline]
 may_lookup fs/namei.c:1958 [inline]
 link_path_walk+0x779/0xe30 fs/namei.c:2601
 path_openat+0x1c6/0x2050 fs/namei.c:4832
 do_file_open+0x16c/0x290 fs/namei.c:4865
 do_sys_openat2+0x94/0x130 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0xf2/0x120 fs/open.c:1383
 x64_sys_call+0x1e39/0x3020 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000009 -> 0x00000008

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 3300 Comm: udevd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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udevd[3300]: inotify_add_watch(7, /dev/loop1p4, 10) failed: No such file or directory
udevd[3300]: inotify_add_watch(7, /dev/loop1p4, 10) failed: No such file or directory