blk-merge: warn if figured out segment number is bigger than nr_phys_segments

We had seen lots of reports of this kind issue, so add one
warnning in blk-merge, then it can be triggered easily and
avoid to depend on warning/bug from drivers.

Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 50793cdc5331..41a55ba0d78e 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -428,6 +428,12 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
         if (sg)
                 sg_mark_end(sg);
 
+        /*
+         * Something must have been wrong if the figured number of
+         * segment is bigger than number of req's physical segments
+         */
+        WARN_ON(nsegs > rq->nr_phys_segments);
+
         return nsegs;
 }
 EXPORT_SYMBOL(blk_rq_map_sg);