syzbot

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BUG: KCSAN: data-race in __put_mountpoint / dput

write to 0xffff88812b802840 of 4 bytes by task 10987 on cpu 1:
 __put_mountpoint+0xef/0x1b0 fs/namespace.c:760
 put_mountpoint fs/namespace.c:771 [inline]
 attach_recursive_mnt+0x446/0x770 fs/namespace.c:2106
 graft_tree+0x10d/0x160 fs/namespace.c:2179
 do_add_mount+0x144/0x1e0 fs/namespace.c:2734
 do_new_mount_fc fs/namespace.c:2771 [inline]
 do_new_mount fs/namespace.c:2824 [inline]
 do_mount+0x12a1/0x14f0 fs/namespace.c:3142
 ksys_mount+0xe8/0x160 fs/namespace.c:3351
 __do_sys_mount fs/namespace.c:3365 [inline]
 __se_sys_mount fs/namespace.c:3362 [inline]
 __x64_sys_mount+0x70/0x90 fs/namespace.c:3362
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88812b802840 of 4 bytes by task 7895 on cpu 0:
 fast_dput fs/dcache.c:727 [inline]
 dput+0x4d/0x750 fs/dcache.c:846
 path_to_nameidata fs/namei.c:830 [inline]
 step_into fs/namei.c:1768 [inline]
 walk_component+0x2e4/0xd90 fs/namei.c:1816
 lookup_last fs/namei.c:2260 [inline]
 path_lookupat.isra.0+0x13a/0x5a0 fs/namei.c:2305
 filename_lookup+0x29e/0x2b0 fs/namei.c:2337
 user_path_at_empty+0x4c/0x70 fs/namei.c:2615
 user_path_at include/linux/namei.h:49 [inline]
 do_utimes+0x161/0x2c0 fs/utimes.c:121
 __do_sys_utimensat fs/utimes.c:153 [inline]
 __se_sys_utimensat fs/utimes.c:137 [inline]
 __x64_sys_utimensat+0x10d/0x180 fs/utimes.c:137
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 7895 Comm: udevd Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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