mm/page_owner: fix memory leak in page_owner_stack_fops->release()

The page_owner_stack_fops->open() callback invokes seq_open_private(),
therefore its corresponding ->release() callback must call
seq_release_private().  Otherwise it will cause a memory leak of struct
stack_print_ctx.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 765973a ("mm,page_owner: display all stacks and their count")
Signed-off-by: Ran Xiaokai <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Brendan Jackman <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ranxiaokai

mm/page_owner.c

@@ -952,7 +952,7 @@ static const struct file_operations page_owner_stack_fops = {
 	.open		= page_owner_stack_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= seq_release,
+	.release	= seq_release_private,
 };
 
 static int page_owner_threshold_get(void *data, u64 *val)