[PATCH] catch errors when completing bio pairs

From: Mike Christie <michaelc@cs.wisc.edu>

A couple of drivers can sometimes fail the first segments in a bio then
requeue the rest of the request.  In this situation, if the last part of
the bio completes successfully bio_pair_end_* will miss that the beginging
of the bio had failed becuase they just return one when bi_size is not yet
zero.  The attached patch moves the error value test before the bi_size to
catch the above case.

fs/bio.c

@@ -701,11 +701,12 @@ static int bio_pair_end_1(struct bio * bi, unsigned int done, int err)
 {
 	struct bio_pair *bp = container_of(bi, struct bio_pair, bio1);
 
-	if (bi->bi_size)
-		return 1;
 	if (err)
 		bp->error = err;
 
+	if (bi->bi_size)
+		return 1;
+
 	bio_pair_release(bp);
 	return 0;
 }
@@ -714,11 +715,12 @@ static int bio_pair_end_2(struct bio * bi, unsigned int done, int err)
 {
 	struct bio_pair *bp = container_of(bi, struct bio_pair, bio2);
 
-	if (bi->bi_size)
-		return 1;
 	if (err)
 		bp->error = err;
 
+	if (bi->bi_size)
+		return 1;
+
 	bio_pair_release(bp);
 	return 0;
 }