1 files changed, 32 insertions, 10 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bb42551c1a42..a03cf2d889bf 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2902,6 +2902,7 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
         struct r5dev *dev = &sh->dev[disk_idx];
         struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
                                   &sh->dev[s->failed_num[1]] };
+        int i;
 
 
         if (test_bit(R5_LOCKED, &dev->flags) ||
@@ -2949,16 +2950,37 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s,
                  * and there is no need to delay that.
                  */
                 return 0;
-        if (
-             (sh->raid_conf->level <= 5 && fdev[0]->towrite &&
-              !test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
-             ((sh->raid_conf->level == 6 ||
-               sh->sector >= sh->raid_conf->mddev->recovery_cp)
-              &&
-              (s->to_write - s->non_overwrite <
-               sh->raid_conf->raid_disks - sh->raid_conf->max_degraded)
-              ))
-                return 1;
+
+        for (i = 0; i < s->failed; i++) {
+                if (fdev[i]->towrite &&
+                    !test_bit(R5_UPTODATE, &fdev[i]->flags) &&
+                    !test_bit(R5_OVERWRITE, &fdev[i]->flags))
+                        /* If we have a partial write to a failed
+                         * device, then we will need to reconstruct
+                         * the content of that device, so all other
+                         * devices must be read.
+                         */
+                        return 1;
+        }
+
+        /* If we are forced to do a reconstruct-write, either because
+         * the current RAID6 implementation only supports that, or
+         * or because parity cannot be trusted and we are currently
+         * recovering it, there is extra need to be careful.
+         * If one of the devices that we would need to read, because
+         * it is not being overwritten (and maybe not written at all)
+         * is missing/faulty, then we need to read everything we can.
+         */
+        if (sh->raid_conf->level != 6 &&
+            sh->sector < sh->raid_conf->mddev->recovery_cp)
+                /* reconstruct-write isn't being forced */
+                return 0;
+        for (i = 0; i < s->failed; i++) {
+                if (!test_bit(R5_UPTODATE, &fdev[i]->flags) &&
+                    !test_bit(R5_OVERWRITE, &fdev[i]->flags))
+                        return 1;
+        }
+
         return 0;
 }