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BUG: KCSAN: data-race in retain_dentry / step_into

write to 0xffff88810d947840 of 4 bytes by task 19683 on cpu 0:
 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_openat fs/open.c:1219 [inline]
 __se_sys_openat fs/open.c:1214 [inline]
 __x64_sys_openat+0xef/0x110 fs/open.c:1214
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88810d947840 of 4 bytes by task 19702 on cpu 1:
 __follow_mount_rcu fs/namei.c:1402 [inline]
 handle_mounts fs/namei.c:1459 [inline]
 step_into+0xec/0xec0 fs/namei.c:1773
 open_last_lookups fs/namei.c:3314 [inline]
 path_openat+0x105e/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_openat fs/open.c:1219 [inline]
 __se_sys_openat fs/open.c:1214 [inline]
 __x64_sys_openat+0xef/0x110 fs/open.c:1214
 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: 1 PID: 19702 Comm: syz-executor.4 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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