syzbot

EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue. Quota mode: writeback.
loop0: detected capacity change from 0 to 4096
EXT4-fs (loop0): mounted filesystem without journal. Opts: ,errors=continue. Quota mode: writeback.
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BUG: KCSAN: data-race in __lookup_mnt / umount_tree

write to 0xffff888129ff8518 of 8 bytes by task 22661 on cpu 0:
 unhash_mnt fs/namespace.c:839 [inline]
 umount_mnt fs/namespace.c:853 [inline]
 umount_tree+0x5c7/0x8f0 fs/namespace.c:1544
 do_umount fs/namespace.c:1664 [inline]
 path_umount+0x9ca/0xa70 fs/namespace.c:1756
 ksys_umount fs/namespace.c:1779 [inline]
 __do_sys_umount fs/namespace.c:1784 [inline]
 __se_sys_umount fs/namespace.c:1782 [inline]
 __x64_sys_umount+0xa6/0xd0 fs/namespace.c:1782
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888129ff8518 of 8 bytes by task 22621 on cpu 1:
 __lookup_mnt+0xa9/0xf0 fs/namespace.c:629
 __follow_mount_rcu fs/namei.c:1422 [inline]
 handle_mounts fs/namei.c:1458 [inline]
 step_into+0x33a/0xec0 fs/namei.c:1772
 walk_component+0x190/0x350 fs/namei.c:1948
 link_path_walk+0x4ba/0x780 fs/namei.c:2265
 path_lookupat+0x7b/0x570 fs/namei.c:2420
 filename_lookup+0xff/0x390 fs/namei.c:2454
 user_path_at_empty+0x3b/0x50 fs/namei.c:2734
 user_path_at include/linux/namei.h:60 [inline]
 path_listxattr fs/xattr.c:768 [inline]
 __do_sys_llistxattr fs/xattr.c:789 [inline]
 __se_sys_llistxattr fs/xattr.c:786 [inline]
 __x64_sys_llistxattr+0x62/0x120 fs/xattr.c:786
 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: 1 PID: 22621 Comm: syz-executor.0 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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