proc: account "struct pde_opener"

The allocation is persistent in fact as any fool can open a file in
/proc and sit on it.

Link: http://lkml.kernel.org/r/20180214082409.GC17157@avx2
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/inode.c

@@ -103,7 +103,7 @@ void __init proc_init_kmemcache(void)
 					     init_once);
 	pde_opener_cache =
 		kmem_cache_create("pde_opener", sizeof(struct pde_opener), 0,
-				  SLAB_PANIC, NULL);
+				  SLAB_ACCOUNT|SLAB_PANIC, NULL);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)