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BUG: KCSAN: data-race in d_set_mounted / traverse_mounts

write to 0xffff8881330d36c0 of 4 bytes by task 26576 on cpu 1:
 d_set_mounted+0x117/0x200 fs/dcache.c:1494
 get_mountpoint+0x1c0/0x350 fs/namespace.c:755
 lock_mount+0x86/0x1d0 fs/namespace.c:2226
 do_loopback fs/namespace.c:2375 [inline]
 path_mount+0xcf8/0x1ce0 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 0xffff8881330d36c0 of 4 bytes by task 26553 on cpu 0:
 __traverse_mounts fs/namei.c:1318 [inline]
 traverse_mounts+0x338/0x410 fs/namei.c:1357
 handle_mounts fs/namei.c:1466 [inline]
 step_into+0x88/0xec0 fs/namei.c:1772
 open_last_lookups fs/namei.c:3308 [inline]
 path_openat+0xfc8/0x20b0 fs/namei.c:3491
 do_filp_open+0xd9/0x1f0 fs/namei.c:3521
 do_sys_openat2+0xa3/0x250 fs/open.c:1187
 do_sys_open fs/open.c:1203 [inline]
 __do_sys_creat fs/open.c:1277 [inline]
 __se_sys_creat fs/open.c:1271 [inline]
 __x64_sys_creat+0x62/0x80 fs/open.c:1271
 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: 26553 Comm: syz-executor.0 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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