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BUG: KCSAN: data-race in lookup_fast / retain_dentry

write to 0xffff88810adc3000 of 4 bytes by task 29167 on cpu 0:
 retain_dentry+0x1de/0x260 fs/dcache.c:659
 dput+0x10e/0x420 fs/dcache.c:880
 path_put+0x1b/0x30 fs/namei.c:496
 tomoyo_realpath_nofollow+0x6b/0x90 security/tomoyo/realpath.c:311
 tomoyo_find_next_domain+0x11d/0x1100 security/tomoyo/domain.c:727
 tomoyo_bprm_check_security+0x96/0xd0 security/tomoyo/tomoyo.c:101
 security_bprm_check+0x3f/0x90 security/security.c:842
 search_binary_handler fs/exec.c:1704 [inline]
 exec_binprm+0x143/0x720 fs/exec.c:1757
 bprm_execve+0x3b8/0x530 fs/exec.c:1826
 kernel_execve+0x626/0x650 fs/exec.c:1969
 call_usermodehelper_exec_async+0x1a1/0x250 kernel/umh.c:110
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

read to 0xffff88810adc3000 of 4 bytes by task 29166 on cpu 1:
 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+0x12d/0x560 fs/namei.c:2336
 filename_lookup+0xf2/0x380 fs/namei.c:2369
 kern_path+0x2e/0x40 fs/namei.c:2456
 tomoyo_realpath_nofollow+0x2f/0x90 security/tomoyo/realpath.c:308
 tomoyo_find_next_domain+0x11d/0x1100 security/tomoyo/domain.c:727
 tomoyo_bprm_check_security+0x96/0xd0 security/tomoyo/tomoyo.c:101
 security_bprm_check+0x3f/0x90 security/security.c:842
 search_binary_handler fs/exec.c:1704 [inline]
 exec_binprm+0x143/0x720 fs/exec.c:1757
 bprm_execve+0x3b8/0x530 fs/exec.c:1826
 kernel_execve+0x626/0x650 fs/exec.c:1969
 call_usermodehelper_exec_async+0x1a1/0x250 kernel/umh.c:110
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29166 Comm: kworker/u4:6 Not tainted 5.11.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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