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BUG: KCSAN: data-race in retain_dentry / step_into

write to 0xffff88810759d000 of 4 bytes by task 11367 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
 do_faccessat+0x3e2/0x500 fs/open.c:457
 __do_sys_access fs/open.c:482 [inline]
 __se_sys_access fs/open.c:480 [inline]
 __x64_sys_access+0x33/0x40 fs/open.c:480
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810759d000 of 4 bytes by task 11365 on cpu 1:
 __follow_mount_rcu fs/namei.c:1316 [inline]
 handle_mounts fs/namei.c:1373 [inline]
 step_into+0xec/0xeb0 fs/namei.c:1691
 walk_component+0x190/0x350 fs/namei.c:1867
 lookup_last fs/namei.c:2312 [inline]
 path_lookupat+0x12d/0x560 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_faccessat+0x260/0x500 fs/open.c:423
 __do_sys_access fs/open.c:482 [inline]
 __se_sys_access fs/open.c:480 [inline]
 __x64_sys_access+0x33/0x40 fs/open.c:480
 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: 11365 Comm: systemd-sysctl 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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