[PATCH] md: improvements to raid5 handling of read errors

Two refinements to the 'attempt-overwrite-on-read-error' mechanism.
1/ If the array is read-only, don't attempt an over-write.
2/ If there are more than max_nr_stripes read errors on a device with
   no success, fail the drive.  This will make sure a dead
   drive will be eventually kicked even when we aren't trying
   to rewrite (which would normally kick a dead drive more quickly.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 21 insertions, 8 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3db5c3513072..3fb80397f8aa 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1582,6 +1582,7 @@ static mdk_rdev_t *md_import_device(dev_t newdev, int super_format, int super_mi
         rdev->in_sync = 0;
         rdev->data_offset = 0;
         atomic_set(&rdev->nr_pending, 0);
+        atomic_set(&rdev->read_errors, 0);
 
         size = rdev->bdev->bd_inode->i_size >> BLOCK_SIZE_BITS;
         if (!size) {
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 08a1620b9f8c..77610b98d4e0 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -420,21 +420,29 @@ static int raid5_end_read_request(struct bio * bi, unsigned int bytes_done,
                         clear_bit(R5_ReadError, &sh->dev[i].flags);
                         clear_bit(R5_ReWrite, &sh->dev[i].flags);
                 }
+                if (atomic_read(&conf->disks[i].rdev->read_errors))
+                        atomic_set(&conf->disks[i].rdev->read_errors, 0);
         } else {
+                int retry = 0;
                 clear_bit(R5_UPTODATE, &sh->dev[i].flags);
-                if (conf->mddev->degraded) {
+                atomic_inc(&conf->disks[i].rdev->read_errors);
+                if (conf->mddev->degraded)
                         printk("R5: read error not correctable.\n");
-                        clear_bit(R5_ReadError, &sh->dev[i].flags);
-                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
-                        md_error(conf->mddev, conf->disks[i].rdev);
-                } else if (test_bit(R5_ReWrite, &sh->dev[i].flags)) {
+                else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                         /* Oh, no!!! */
                         printk("R5: read error NOT corrected!!\n");
+                else if (atomic_read(&conf->disks[i].rdev->read_errors)
+                         > conf->max_nr_stripes)
+                        printk("raid5: Too many read errors, failing device.\n");
+                else
+                        retry = 1;
+                if (retry)
+                        set_bit(R5_ReadError, &sh->dev[i].flags);
+                else {
                         clear_bit(R5_ReadError, &sh->dev[i].flags);
                         clear_bit(R5_ReWrite, &sh->dev[i].flags);
                         md_error(conf->mddev, conf->disks[i].rdev);
-                } else
-                        set_bit(R5_ReadError, &sh->dev[i].flags);
+                }
         }
         rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
 #if 0
@@ -1328,7 +1336,8 @@ static void handle_stripe(struct stripe_head *sh)
         /* If the failed drive is just a ReadError, then we might need to progress
          * the repair/check process
          */
-        if (failed == 1 && test_bit(R5_ReadError, &sh->dev[failed_num].flags)
+        if (failed == 1 && ! conf->mddev->ro &&
+            test_bit(R5_ReadError, &sh->dev[failed_num].flags)
             && !test_bit(R5_LOCKED, &sh->dev[failed_num].flags)
             && test_bit(R5_UPTODATE, &sh->dev[failed_num].flags)
                 ) {
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 4169c11e5451..200c69e34fc0 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -134,6 +134,9 @@ struct mdk_rdev_s
                                          * only maintained for arrays that
                                          * support hot removal
                                          */
+        atomic_t        read_errors;    /* number of consecutive read errors that
+                                         * we have tried to ignore.
+                                         */
 };
 
 typedef struct mdk_personality_s mdk_personality_t;