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BUG: KCSAN: data-race in __put_mountpoint / dput

read to 0xffff8881251d7f00 of 4 bytes by task 24859 on cpu 1:
 fast_dput fs/dcache.c:727 [inline]
 dput+0x4d/0x750 fs/dcache.c:846
 path_put fs/namei.c:482 [inline]
 terminate_walk+0x107/0x250 fs/namei.c:596
 path_openat+0xfff/0x36e0 fs/namei.c:3529
 do_filp_open+0x11e/0x1b0 fs/namei.c:3555
 do_sys_open+0x3b3/0x4f0 fs/open.c:1097
 __do_sys_open fs/open.c:1115 [inline]
 __se_sys_open fs/open.c:1110 [inline]
 __x64_sys_open+0x55/0x70 fs/open.c:1110
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8881251d7f00 of 4 bytes by task 24857 on cpu 0:
 __put_mountpoint+0xef/0x1b0 fs/namespace.c:760
 put_mountpoint fs/namespace.c:771 [inline]
 unlock_mount+0x42/0x80 fs/namespace.c:2163
 do_add_mount+0x154/0x1e0 fs/namespace.c:2735
 do_new_mount_fc fs/namespace.c:2767 [inline]
 do_new_mount fs/namespace.c:2825 [inline]
 do_mount+0x12e7/0x1560 fs/namespace.c:3143
 ksys_mount+0xe8/0x160 fs/namespace.c:3352
 __do_sys_mount fs/namespace.c:3366 [inline]
 __se_sys_mount fs/namespace.c:3363 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3363
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 24857 Comm: syz-executor.1 Not tainted 5.4.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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