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BUG: KCSAN: data-race in __dentry_kill / retain_dentry

write to 0xffff88810d0b6d80 of 4 bytes by task 10796 on cpu 0:
 d_lru_add fs/dcache.c:400 [inline]
 retain_dentry+0x17f/0x240 fs/dcache.c:657
 dput+0x10e/0x420 fs/dcache.c:873
 __fput+0x395/0x4d0 fs/file_table.c:294
 ____fput+0x11/0x20 fs/file_table.c:314
 task_work_run+0x8e/0x110 kernel/task_work.c:141
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:165 [inline]
 exit_to_user_mode_prepare+0x1a4/0x200 kernel/entry/common.c:192
 syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:267
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810d0b6d80 of 4 bytes by task 10800 on cpu 1:
 dentry_unlist fs/dcache.c:544 [inline]
 __dentry_kill+0x1e7/0x450 fs/dcache.c:575
 dentry_kill fs/dcache.c:692 [inline]
 dput+0x203/0x420 fs/dcache.c:878
 __lookup_slow+0x21f/0x250 fs/namei.c:1547
 lookup_slow fs/namei.c:1561 [inline]
 walk_component+0x2a5/0x350 fs/namei.c:1860
 lookup_last fs/namei.c:2309 [inline]
 path_lookupat+0x11d/0x550 fs/namei.c:2333
 filename_lookup+0xf2/0x380 fs/namei.c:2366
 user_path_at_empty+0x3b/0x50 fs/namei.c:2646
 user_path_at include/linux/namei.h:59 [inline]
 do_utimes_path fs/utimes.c:93 [inline]
 do_utimes fs/utimes.c:143 [inline]
 __do_sys_utime fs/utimes.c:224 [inline]
 __se_sys_utime+0xd8/0x1c0 fs/utimes.c:213
 __x64_sys_utime+0x2d/0x40 fs/utimes.c:213
 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: 1 PID: 10800 Comm: syz-executor.0 Not tainted 5.9.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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