[PATCH] mm, swap: Potential NULL dereference in get_swap_page_of_type()

[Dan Carpenter <dan.carpenter@oracle.com>]

Smatch complains that the NULL checks on "si" aren't consistent.  This
seems like a real bug because we have not ensured that the type is
valid and so "si" can be NULL.

Fixes: ec8acf20afb8 ("swap: add per-partition lock for swapfile")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 mm/swapfile.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f0edf7244256..21e92c757205 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1048,9 +1048,12 @@ swp_entry_t get_swap_page_of_type(int type)
 	struct swap_info_struct *si;
 	pgoff_t offset;
 
+	if (type >= nr_swapfiles)
+		goto fail;
+
 	si = swap_info[type];
 	spin_lock(&si->lock);
-	if (si && (si->flags & SWP_WRITEOK)) {
+	if (si->flags & SWP_WRITEOK) {
 		atomic_long_dec(&nr_swap_pages);
 		/* This is called for allocating swap entry, not cache */
 		offset = scan_swap_map(si, 1);
@@ -1061,6 +1064,7 @@ swp_entry_t get_swap_page_of_type(int type)
 		atomic_long_inc(&nr_swap_pages);
 	}
 	spin_unlock(&si->lock);
+fail:
 	return (swp_entry_t) {0};
 }
 
-- 
2.17.1