[PATCH] direct-io: Prevent NULL pointer access in submit_page_section

[Andreas Gruenbacher]

In the code added to function submit_page_section by commit b1058b981,
sdio->bio can currently be NULL when calling dio_bio_submit.  This then
leads to a NULL pointer access in dio_bio_submit, so check for a NULL
bio in submit_page_section before trying to submit it instead.

Fixes xfstest generic/250 on gfs2.

Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 5fa2211e49ae..e0332da392d8 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -838,7 +838,8 @@ submit_page_section(struct dio *dio, struct dio_submit *sdio, struct page *page,
 	 */
 	if (sdio->boundary) {
 		ret = dio_send_cur_page(dio, sdio, map_bh);
-		dio_bio_submit(dio, sdio);
+		if (sdio->bio)
+			dio_bio_submit(dio, sdio);
 		put_page(sdio->cur_page);
 		sdio->cur_page = NULL;
 	}
-- 
2.13.5