[PATCH 3.16 099/204] direct-io: Prevent NULL pointer access in submit_page_section

[Ben Hutchings]

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Gruenbacher <agrue...@redhat.com>

commit 899f0429c7d3eed886406cd72182bee3b96aa1f9 upstream.

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 <agrue...@redhat.com>
Reviewed-by: Jan Kara <j...@suse.cz>
Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
 fs/direct-io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -812,7 +812,8 @@ out:
         */
        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);
                page_cache_release(sdio->cur_page);
                sdio->cur_page = NULL;
        }