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BUG: KCSAN: data-race in __lookup_mnt / umount_tree

write to 0xffff88813948f798 of 8 bytes by task 20593 on cpu 0:
 unhash_mnt fs/namespace.c:884 [inline]
 umount_mnt fs/namespace.c:898 [inline]
 umount_tree+0x5c7/0x8f0 fs/namespace.c:1594
 path_umount+0x9df/0xa70 fs/namespace.c:1802
 ksys_umount fs/namespace.c:1825 [inline]
 __do_sys_umount fs/namespace.c:1830 [inline]
 __se_sys_umount fs/namespace.c:1828 [inline]
 __x64_sys_umount+0xb5/0xe0 fs/namespace.c:1828
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88813948f798 of 8 bytes by task 20591 on cpu 1:
 __lookup_mnt+0xa9/0xf0 fs/namespace.c:674
 __follow_mount_rcu fs/namei.c:1500 [inline]
 handle_mounts fs/namei.c:1536 [inline]
 step_into+0x35c/0xf70 fs/namei.c:1850
 walk_component+0x1a1/0x360 fs/namei.c:2026
 lookup_last fs/namei.c:2475 [inline]
 path_lookupat+0x12d/0x3d0 fs/namei.c:2499
 filename_lookup+0x130/0x310 fs/namei.c:2528
 user_path_at_empty+0x3e/0x110 fs/namei.c:2851
 user_path_at include/linux/namei.h:57 [inline]
 do_mount fs/namespace.c:3380 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount+0x217/0x2f0 fs/namespace.c:3568
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x50 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0xffff88812229ae40 -> 0xffff88814641ccc0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 20591 Comm: syz-executor.2 Not tainted 5.17.0-syzkaller-14114-g09bb8856d4a7-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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