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BUG: KCSAN: data-race in __d_instantiate / lookup_fast

read to 0xffff88812508ba80 of 4 bytes by task 28553 on cpu 1:
 d_is_miss include/linux/dcache.h:394 [inline]
 d_is_negative include/linux/dcache.h:440 [inline]
 lookup_fast+0xdf/0x6c0 fs/namei.c:1581
 walk_component+0x6d/0xd90 fs/namei.c:1798
 lookup_last fs/namei.c:2260 [inline]
 path_lookupat.isra.0+0x13a/0x5a0 fs/namei.c:2305
 filename_lookup+0x145/0x2b0 fs/namei.c:2335
 user_path_at_empty+0x4c/0x70 fs/namei.c:2615
 user_path_at include/linux/namei.h:49 [inline]
 do_mount+0xc8/0x14f0 fs/namespace.c:3080
 ksys_mount+0xe8/0x160 fs/namespace.c:3351
 __do_sys_mount fs/namespace.c:3365 [inline]
 __se_sys_mount fs/namespace.c:3362 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3362
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812508ba80 of 4 bytes by task 28550 on cpu 0:
 fsnotify_update_flags include/linux/fsnotify_backend.h:390 [inline]
 __d_instantiate+0x291/0x2f0 fs/dcache.c:1931
 d_instantiate_new+0x7c/0x100 fs/dcache.c:1975
 ext4_add_nondir+0x140/0x190 fs/ext4/namei.c:2566
 ext4_create+0x177/0x300 fs/ext4/namei.c:2606
 lookup_open fs/namei.c:3241 [inline]
 do_last fs/namei.c:3331 [inline]
 path_openat+0x2b10/0x3580 fs/namei.c:3537
 do_filp_open+0x11e/0x1b0 fs/namei.c:3567
 do_sys_open+0x3b3/0x4f0 fs/open.c:1097
 __do_sys_open fs/open.c:1115 [inline]
 __se_sys_open fs/open.c:1110 [inline]
 __x64_sys_open+0x55/0x70 fs/open.c:1110
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 28550 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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