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BUG: KCSAN: data-race in d_set_mounted / fast_dput

write to 0xffff888100456780 of 4 bytes by task 15658 on cpu 1:
 d_set_mounted+0x117/0x200 fs/dcache.c:1494
 get_mountpoint+0x1c0/0x350 fs/namespace.c:755
 attach_recursive_mnt+0x9a/0x1230 fs/namespace.c:2140
 graft_tree fs/namespace.c:2263 [inline]
 do_loopback fs/namespace.c:2391 [inline]
 path_mount+0x1299/0x1ce0 fs/namespace.c:3229
 do_mount fs/namespace.c:3248 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3433
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3433
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888100456780 of 4 bytes by task 15654 on cpu 0:
 fast_dput+0x14/0x1c0 fs/dcache.c:749
 dput+0x26/0x360 fs/dcache.c:875
 path_put fs/namei.c:546 [inline]
 terminate_walk+0x218/0x270 fs/namei.c:649
 path_openat+0x1968/0x20b0 fs/namei.c:3495
 do_filp_open+0x1b6/0x1f0 fs/namei.c:3523
 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+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15654 Comm: syz-executor.4 Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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