KCSAN: data-race in lookup_fast / retain

similar bugs (4):
Kernel	Title	Count	Last	Reported	Patched	Status
upstream	KCSAN: data-race in lookup_fast / retain_dentry (4)	4	541d	592d	0/23	auto-closed as invalid on 2021/03/27 05:59
upstream	KCSAN: data-race in lookup_fast / retain_dentry	2	725d	737d	0/23	auto-closed as invalid on 2020/09/23 11:25
upstream	KCSAN: data-race in lookup_fast / retain_dentry (2)	1	687d	687d	0/23	auto-closed as invalid on 2020/10/31 17:53
upstream	KCSAN: data-race in lookup_fast / retain_dentry (3)	2	631d	615d	0/23	auto-closed as invalid on 2020/12/27 03:33

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BUG: KCSAN: data-race in lookup_fast / retain_dentry

write to 0xffff8880264f7c00 of 4 bytes by task 27320 on cpu 1:
 retain_dentry+0x1de/0x260 fs/dcache.c:660
 dput+0x11e/0x430 fs/dcache.c:881
 path_put fs/namei.c:546 [inline]
 terminate_walk+0x109/0x270 fs/namei.c:645
 path_openat+0x18dc/0x21b0 fs/namei.c:3501
 do_filp_open+0xd9/0x1f0 fs/namei.c:3527
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1207
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8880264f7c00 of 4 bytes by task 27324 on cpu 0:
 d_revalidate fs/namei.c:826 [inline]
 lookup_fast+0x15f/0x350 fs/namei.c:1579
 open_last_lookups fs/namei.c:3260 [inline]
 path_openat+0x47e/0x21b0 fs/namei.c:3497
 do_filp_open+0xd9/0x1f0 fs/namei.c:3527
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_open fs/open.c:1211 [inline]
 __se_sys_open fs/open.c:1207 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1207
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27324 Comm: syz-executor.2 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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