mm/swap.c:put_pages_list(): reinitialise the page list

While free_unref_page_list() puts pages onto the CPU local LRU list, it
does not remove them from the list they were passed in on.  That makes
the list_head appear to be non-empty, and would lead to various
corruption problems if we didn't have an assertion that the list was
empty.

Reinitialise the list after calling free_unref_page_list() to avoid this
problem.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 988c69f ("mm: optimise put_pages_list()")
Signed-off-by: Matthew Wilcox (Oracle) <[email protected]>
Reviewed-by: Steve French <[email protected]>
Reported-by: Namjae Jeon <[email protected]>
Tested-by: Steve French <[email protected]>
Tested-by: Namjae Jeon <[email protected]>
Cc: Steve French <[email protected]>
Cc: Hyeoncheol Lee <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/swap.c

@@ -156,6 +156,7 @@ void put_pages_list(struct list_head *pages)
 	}
 
 	free_unref_page_list(pages);
+	INIT_LIST_HEAD(pages);
 }
 EXPORT_SYMBOL(put_pages_list);