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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff88811b936240 of 4 bytes by task 23522 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:1977
 d_make_persistent+0x78/0x110 fs/dcache.c:2793
 shmem_mknod+0x15f/0x170 mm/shmem.c:3892
 shmem_create+0x34/0x50 mm/shmem.c:3943
 lookup_open fs/namei.c:4449 [inline]
 open_last_lookups fs/namei.c:4549 [inline]
 path_openat+0x1121/0x23c0 fs/namei.c:4793
 do_filp_open+0x15d/0x280 fs/namei.c:4823
 do_sys_openat2+0xa6/0x150 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_open fs/open.c:1444 [inline]
 __se_sys_open fs/open.c:1440 [inline]
 __x64_sys_open+0xe6/0x110 fs/open.c:1440
 x64_sys_call+0x166f/0x3000 arch/x86/include/generated/asm/syscalls_64.h:3
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811b936240 of 4 bytes by task 23520 on cpu 1:
 d_revalidate fs/namei.c:976 [inline]
 lookup_fast+0xf0/0x320 fs/namei.c:1814
 lookup_fast_for_open fs/namei.c:4486 [inline]
 open_last_lookups fs/namei.c:4520 [inline]
 path_openat+0x415/0x23c0 fs/namei.c:4793
 do_filp_open+0x15d/0x280 fs/namei.c:4823
 do_sys_openat2+0xa6/0x150 fs/open.c:1430
 do_sys_open fs/open.c:1436 [inline]
 __do_sys_open fs/open.c:1444 [inline]
 __se_sys_open fs/open.c:1440 [inline]
 __x64_sys_open+0xe6/0x110 fs/open.c:1440
 x64_sys_call+0x166f/0x3000 arch/x86/include/generated/asm/syscalls_64.h:3
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc0/0x2a0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000080 -> 0x08200080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 23520 Comm: syz.8.4849 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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