4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Vitaly Mayatskikh <v.mayatskih@xxxxxxxxx>
commit 95d78c28b5a85bacbc29b8dba7c04babb9b0d467 upstream.
bio_map_user_iov and bio_unmap_user do unbalanced pages refcounting if
IO vector has small consecutive buffers belonging to the same page.
bio_add_pc_page merges them into one, but the page reference is never
dropped.
Signed-off-by: Vitaly Mayatskikh <v.mayatskih@xxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
block/bio.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/block/bio.c
+++ b/block/bio.c
@@ -1318,6 +1318,7 @@ struct bio *bio_map_user_iov(struct requ
offset = offset_in_page(uaddr);
for (j = cur_page; j < page_limit; j++) {
unsigned int bytes = PAGE_SIZE - offset;
+ unsigned short prev_bi_vcnt = bio->bi_vcnt;
if (len <= 0)
break;
@@ -1332,6 +1333,13 @@ struct bio *bio_map_user_iov(struct requ
bytes)
break;
+ /*
+ * check if vector was merged with previous
+ * drop page reference if needed
+ */
+ if (bio->bi_vcnt == prev_bi_vcnt)
+ put_page(pages[j]);
+
len -= bytes;
offset = 0;
}