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BUG: KCSAN: data-race in __dentry_kill / d_alloc_parallel

write to 0xffff8881214caa80 of 4 bytes by task 7606 on cpu 0:
 d_alloc_parallel+0xb5b/0xd10 fs/dcache.c:2631
 lookup_open fs/namei.c:3030 [inline]
 open_last_lookups fs/namei.c:3177 [inline]
 path_openat+0x665/0x20a0 fs/namei.c:3365
 do_filp_open+0xbd/0x1d0 fs/namei.c:3395
 do_sys_openat2+0x33b/0x500 fs/open.c:1168
 do_sys_open fs/open.c:1184 [inline]
 __do_sys_open fs/open.c:1192 [inline]
 __se_sys_open fs/open.c:1188 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1188
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8881214caa80 of 4 bytes by task 7653 on cpu 1:
 dentry_unlist fs/dcache.c:544 [inline]
 __dentry_kill+0x1ef/0x450 fs/dcache.c:575
 dentry_kill fs/dcache.c:692 [inline]
 dput+0x208/0x420 fs/dcache.c:878
 handle_mounts fs/namei.c:1389 [inline]
 step_into+0x448/0xe70 fs/namei.c:1690
 open_last_lookups fs/namei.c:3200 [inline]
 path_openat+0xfaf/0x20a0 fs/namei.c:3365
 do_filp_open+0xbd/0x1d0 fs/namei.c:3395
 do_sys_openat2+0x33b/0x500 fs/open.c:1168
 do_sys_open fs/open.c:1184 [inline]
 __do_sys_open fs/open.c:1192 [inline]
 __se_sys_open fs/open.c:1188 [inline]
 __x64_sys_open+0xe2/0x110 fs/open.c:1188
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 7653 Comm: systemd-udevd Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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