md/raid1: fix bio handling problems in process_checks()

Recent change to use bio_copy_data() in raid1 when repairing
an array is faulty.

The underlying may have changed the bio in various ways using
bio_advance and these need to be undone not just for the 'sbio' which
is being copied to, but also the 'pbio' (primary) which is being
copied from.

So perform the reset on all bios that were read from and do it early.

This also ensure that the sbio->bi_io_vec[j].bv_len passed to
memcmp is correct.

This fixes a crash during a 'check' of a RAID1 array.  The crash was
introduced in 3.10 so this is suitable for 3.10-stable.

Cc: stable@vger.kernel.org (3.10)
Reported-by: NJoe Lawrence <joe.lawrence@stratus.com>
Signed-off-by: NNeilBrown <neilb@suse.de>

drivers/md/raid1.c

@@ -1849,6 +1849,36 @@ static int process_checks(struct r1bio *r1_bio)
 	int i;
 	int vcnt;
 
+	/* Fix variable parts of all bios */
+	vcnt = (r1_bio->sectors + PAGE_SIZE / 512 - 1) >> (PAGE_SHIFT - 9);
+	for (i = 0; i < conf->raid_disks * 2; i++) {
+		int j;
+		int size;
+		struct bio *b = r1_bio->bios[i];
+		if (b->bi_end_io != end_sync_read)
+			continue;
+		/* fixup the bio for reuse */
+		bio_reset(b);
+		b->bi_vcnt = vcnt;
+		b->bi_size = r1_bio->sectors << 9;
+		b->bi_sector = r1_bio->sector +
+			conf->mirrors[i].rdev->data_offset;
+		b->bi_bdev = conf->mirrors[i].rdev->bdev;
+		b->bi_end_io = end_sync_read;
+		b->bi_private = r1_bio;
+
+		size = b->bi_size;
+		for (j = 0; j < vcnt ; j++) {
+			struct bio_vec *bi;
+			bi = &b->bi_io_vec[j];
+			bi->bv_offset = 0;
+			if (size > PAGE_SIZE)
+				bi->bv_len = PAGE_SIZE;
+			else
+				bi->bv_len = size;
+			size -= PAGE_SIZE;
+		}
+	}
 	for (primary = 0; primary < conf->raid_disks * 2; primary++)
 		if (r1_bio->bios[primary]->bi_end_io == end_sync_read &&
 		    test_bit(BIO_UPTODATE, &r1_bio->bios[primary]->bi_flags)) {
@@ -1857,12 +1887,10 @@ static int process_checks(struct r1bio *r1_bio)
 			break;
 		}
 	r1_bio->read_disk = primary;
-	vcnt = (r1_bio->sectors + PAGE_SIZE / 512 - 1) >> (PAGE_SHIFT - 9);
 	for (i = 0; i < conf->raid_disks * 2; i++) {
 		int j;
 		struct bio *pbio = r1_bio->bios[primary];
 		struct bio *sbio = r1_bio->bios[i];
-		int size;
 
 		if (sbio->bi_end_io != end_sync_read)
 			continue;
@@ -1888,27 +1916,6 @@ static int process_checks(struct r1bio *r1_bio)
 			rdev_dec_pending(conf->mirrors[i].rdev, mddev);
 			continue;
 		}
-		/* fixup the bio for reuse */
-		bio_reset(sbio);
-		sbio->bi_vcnt = vcnt;
-		sbio->bi_size = r1_bio->sectors << 9;
-		sbio->bi_sector = r1_bio->sector +
-			conf->mirrors[i].rdev->data_offset;
-		sbio->bi_bdev = conf->mirrors[i].rdev->bdev;
-		sbio->bi_end_io = end_sync_read;
-		sbio->bi_private = r1_bio;
-
-		size = sbio->bi_size;
-		for (j = 0; j < vcnt ; j++) {
-			struct bio_vec *bi;
-			bi = &sbio->bi_io_vec[j];
-			bi->bv_offset = 0;
-			if (size > PAGE_SIZE)
-				bi->bv_len = PAGE_SIZE;
-			else
-				bi->bv_len = size;
-			size -= PAGE_SIZE;
-		}
 
 		bio_copy_data(sbio, pbio);
 	}