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BUG: KCSAN: data-race in d_set_mounted / dput

write to 0xffff8881370759c0 of 4 bytes by task 19157 on cpu 0:
 d_set_mounted+0x112/0x190 fs/dcache.c:1459
 get_mountpoint+0x1ac/0x2f0 fs/namespace.c:740
 lock_mount+0x86/0x1d0 fs/namespace.c:2200
 do_loopback fs/namespace.c:2349 [inline]
 path_mount+0xbb1/0x1c10 fs/namespace.c:3199
 do_mount fs/namespace.c:3218 [inline]
 __do_sys_mount fs/namespace.c:3426 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3403
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3403
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881370759c0 of 4 bytes by task 19147 on cpu 1:
 fast_dput fs/dcache.c:746 [inline]
 dput+0x2f/0x420 fs/dcache.c:865
 path_put fs/namei.c:496 [inline]
 terminate_walk+0x109/0x260 fs/namei.c:593
 path_lookupat+0x2c5/0x550 fs/namei.c:2351
 filename_lookup+0xf2/0x380 fs/namei.c:2367
 user_path_at_empty+0x3b/0x50 fs/namei.c:2647
 user_path_at include/linux/namei.h:59 [inline]
 path_setxattr+0x4c/0x170 fs/xattr.c:562
 __do_sys_setxattr fs/xattr.c:582 [inline]
 __se_sys_setxattr fs/xattr.c:578 [inline]
 __x64_sys_setxattr+0x69/0x80 fs/xattr.c:578
 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: 19147 Comm: syz-executor.5 Not tainted 5.10.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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