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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read-write to 0xffff8881004133c0 of 4 bytes by task 5764 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:-1 [inline]
 __d_instantiate+0x2a8/0x390 fs/dcache.c:1987
 d_make_persistent+0x78/0x110 fs/dcache.c:2803
 shmem_mknod+0x15f/0x170 mm/shmem.c:3921
 shmem_create+0x34/0x50 mm/shmem.c:3972
 lookup_open fs/namei.c:4483 [inline]
 open_last_lookups fs/namei.c:4583 [inline]
 path_openat+0xd75/0x2050 fs/namei.c:4827
 do_file_open+0x16c/0x290 fs/namei.c:4859
 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

read to 0xffff8881004133c0 of 4 bytes by task 5765 on cpu 1:
 d_revalidate fs/namei.c:1029 [inline]
 lookup_fast+0xf0/0x320 fs/namei.c:1864
 lookup_fast_for_open fs/namei.c:4520 [inline]
 open_last_lookups fs/namei.c:4554 [inline]
 path_openat+0x436/0x2050 fs/namei.c:4827
 do_file_open+0x16c/0x290 fs/namei.c:4859
 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: 0x00000080 -> 0x08200080

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5765 Comm: syz.4.659 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
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vlan3: entered promiscuous mode
veth0: entered promiscuous mode