syzbot

BUG: KCSAN: data-race in d_set_mounted / path_lookupat

write to 0xffff88813361f0c0 of 4 bytes by task 8719 on cpu 0:
 d_set_mounted+0x117/0x200 fs/dcache.c:1492
 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 0xffff88813361f0c0 of 4 bytes by task 8714 on cpu 1:
 complete_walk fs/namei.c:883 [inline]
 path_lookupat+0x3d0/0x570 fs/namei.c:2428
 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]
 do_mount fs/namespace.c:3245 [inline]
 __do_sys_mount fs/namespace.c:3456 [inline]
 __se_sys_mount+0x209/0x2e0 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8714 Comm: syz-executor.3 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================
9pnet: Insufficient options for proto=fd