A KMSAN warning is reported by Alexander Potapenko:

BUG: KMSAN: uninit-value in kernfs_dop_revalidate+0x61f/0x840
fs/kernfs/dir.c:1053
 kernfs_dop_revalidate+0x61f/0x840 fs/kernfs/dir.c:1053
 d_revalidate fs/namei.c:854
 lookup_dcache fs/namei.c:1522
 __lookup_hash+0x3a6/0x590 fs/namei.c:1543
 filename_create+0x312/0x7c0 fs/namei.c:3657
 do_mkdirat+0x103/0x930 fs/namei.c:3900
 __do_sys_mkdir fs/namei.c:3931
 __se_sys_mkdir fs/namei.c:3929
 __x64_sys_mkdir+0xda/0x120 fs/namei.c:3929
 do_syscall_x64 arch/x86/entry/common.c:51

It seems a positive dentry in kernfs becomes a negative dentry directly
through d_delete() in vfs_rmdir(). dentry->d_time is uninitialized
when accessing it in kernfs_dop_revalidate(), because it is only
initialized when created as negative dentry in kernfs_iop_lookup().

The problem can be reproduced by the following command:

  cd /sys/fs/cgroup/pids && mkdir hi && stat hi && rmdir hi && stat hi

A simple fixes seems to be init...