md/raid1: perform bad-block tests for WriteMostly devices too.

We normally try to avoid reading from write-mostly devices, but when
we do we really have to check for bad blocks and be sure not to
try reading them.

With the current code, best_good_sectors might not get set and that
causes zero-length read requests to be send down which is very
confusing.

This bug was introduced in commit d2eb35acfdccbe2 and so the patch
is suitable for 3.1.x and 3.2.x

Reported-and-tested-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Reported-and-tested-by: Art -kwaak- van Breemen <ard@telegraafnet.nl>
Signed-off-by: NeilBrown <neilb@suse.de>
Cc: stable@vger.kernel.org

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index cc24f0c..a368db2 100644 (file)
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -531,8 +531,17 @@ static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sect
                if (test_bit(WriteMostly, &rdev->flags)) {
                        /* Don't balance among write-mostly, just
                         * use the first as a last resort */
-                       if (best_disk < 0)
+                       if (best_disk < 0) {
+                               if (is_badblock(rdev, this_sector, sectors,
+                                               &first_bad, &bad_sectors)) {
+                                       if (first_bad < this_sector)
+                                               /* Cannot use this */
+                                               continue;
+                                       best_good_sectors = first_bad - this_sector;
+                               } else
+                                       best_good_sectors = sectors;
                                best_disk = disk;
+                       }
                        continue;
                }
                /* This is a reasonable device to use.  It might