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BUG: KCSAN: data-race in lookup_fast / retain_dentry

write to 0xffff8880094f1780 of 4 bytes by task 21258 on cpu 1:
 d_lru_add fs/dcache.c:400 [inline]
 retain_dentry+0x17f/0x240 fs/dcache.c:657
 dput+0x10e/0x420 fs/dcache.c:880
 path_put+0x1b/0x30 fs/namei.c:496
 path_setxattr+0xe4/0x170 fs/xattr.c:575
 __do_sys_lsetxattr fs/xattr.c:594 [inline]
 __se_sys_lsetxattr fs/xattr.c:590 [inline]
 __x64_sys_lsetxattr+0x66/0x80 fs/xattr.c:590
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880094f1780 of 4 bytes by task 21273 on cpu 0:
 d_revalidate fs/namei.c:767 [inline]
 lookup_fast+0x15f/0x370 fs/namei.c:1493
 walk_component+0x5c/0x350 fs/namei.c:1857
 lookup_last fs/namei.c:2312 [inline]
 path_lookupat+0x11d/0x550 fs/namei.c:2336
 filename_lookup+0xf2/0x380 fs/namei.c:2369
 user_path_at_empty+0x3b/0x50 fs/namei.c:2649
 user_path_at include/linux/namei.h:59 [inline]
 do_fchmodat fs/open.c:619 [inline]
 __do_sys_chmod fs/open.c:639 [inline]
 __se_sys_chmod fs/open.c:637 [inline]
 __x64_sys_chmod+0x5a/0x110 fs/open.c:637
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 21273 Comm: syz-executor.4 Not tainted 5.11.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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