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BUG: KCSAN: data-race in d_set_mounted / link_path_walk

write to 0xffff888101776c00 of 4 bytes by task 4376 on cpu 1:
 d_set_mounted+0x117/0x200 fs/dcache.c:1492
 get_mountpoint+0x1c0/0x350 fs/namespace.c:755
 lock_mount+0x86/0x1d0 fs/namespace.c:2224
 do_loopback fs/namespace.c:2373 [inline]
 path_mount+0xcf8/0x1ce0 fs/namespace.c:3227
 do_mount fs/namespace.c:3246 [inline]
 __do_sys_mount fs/namespace.c:3454 [inline]
 __se_sys_mount+0x23d/0x2e0 fs/namespace.c:3431
 __x64_sys_mount+0x63/0x70 fs/namespace.c:3431
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888101776c00 of 4 bytes by task 1026 on cpu 0:
 link_path_walk+0x37d/0x780 fs/namei.c:2232
 path_lookupat+0x7b/0x570 fs/namei.c:2421
 filename_lookup+0xff/0x390 fs/namei.c:2455
 user_path_at_empty+0x3b/0x50 fs/namei.c:2735
 user_path_at include/linux/namei.h:60 [inline]
 vfs_statx+0x98/0x290 fs/stat.c:195
 vfs_fstatat fs/stat.c:217 [inline]
 vfs_lstat include/linux/fs.h:3240 [inline]
 __do_sys_newlstat fs/stat.c:372 [inline]
 __se_sys_newlstat+0x46/0x250 fs/stat.c:366
 __x64_sys_newlstat+0x2d/0x40 fs/stat.c:366
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1026 Comm: systemd-udevd Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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