2 files changed, 30 insertions, 6 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index bb4b12e370df..3bbc6d647044 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3766,7 +3766,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
         int new_data_disks = conf->raid_disks - conf->max_degraded;
         int i;
         int dd_idx;
-        sector_t writepos, safepos, gap;
+        sector_t writepos, readpos, safepos;
         sector_t stripe_addr;
         int reshape_sectors;
         struct list_head stripes;
@@ -3806,26 +3806,46 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
          */
         writepos = conf->reshape_progress;
         sector_div(writepos, new_data_disks);
+        readpos = conf->reshape_progress;
+        sector_div(readpos, data_disks);
         safepos = conf->reshape_safe;
         sector_div(safepos, data_disks);
         if (mddev->delta_disks < 0) {
                 writepos -= reshape_sectors;
+                readpos += reshape_sectors;
                 safepos += reshape_sectors;
-                gap = conf->reshape_safe - conf->reshape_progress;
         } else {
                 writepos += reshape_sectors;
+                readpos -= reshape_sectors;
                 safepos -= reshape_sectors;
-                gap = conf->reshape_progress - conf->reshape_safe;
         }
 
+        /* 'writepos' is the most advanced device address we might write.
+         * 'readpos' is the least advanced device address we might read.
+         * 'safepos' is the least address recorded in the metadata as having
+         *     been reshaped.
+         * If 'readpos' is behind 'writepos', then there is no way that we can
+         * ensure safety in the face of a crash - that must be done by userspace
+         * making a backup of the data.  So in that case there is no particular
+         * rush to update metadata.
+         * Otherwise if 'safepos' is behind 'writepos', then we really need to
+         * update the metadata to advance 'safepos' to match 'readpos' so that
+         * we can be safe in the event of a crash.
+         * So we insist on updating metadata if safepos is behind writepos and
+         * readpos is beyond writepos.
+         * In any case, update the metadata every 10 seconds.
+         * Maybe that number should be configurable, but I'm not sure it is
+         * worth it.... maybe it could be a multiple of safemode_delay???
+         */
         if ((mddev->delta_disks < 0
-             ? writepos < safepos
-             : writepos > safepos) ||
-            gap > (new_data_disks)*3000*2 /*3Meg*/) {
+             ? (safepos > writepos && readpos < writepos)
+             : (safepos < writepos && readpos > writepos)) ||
+            time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
                 /* Cannot proceed until we've updated the superblock... */
                 wait_event(conf->wait_for_overlap,
                            atomic_read(&conf->reshape_stripes)==0);
                 mddev->reshape_position = conf->reshape_progress;
+                conf->reshape_checkpoint = jiffies;
                 set_bit(MD_CHANGE_DEVS, &mddev->flags);
                 md_wakeup_thread(mddev->thread);
                 wait_event(mddev->sb_wait, mddev->flags == 0 ||
@@ -3923,6 +3943,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
                 wait_event(conf->wait_for_overlap,
                            atomic_read(&conf->reshape_stripes) == 0);
                 mddev->reshape_position = conf->reshape_progress;
+                conf->reshape_checkpoint = jiffies;
                 set_bit(MD_CHANGE_DEVS, &mddev->flags);
                 md_wakeup_thread(mddev->thread);
                 wait_event(mddev->sb_wait,
@@ -4957,6 +4978,7 @@ static int raid5_start_reshape(mddev_t *mddev)
                 spin_unlock_irq(&conf->device_lock);
                 return -EAGAIN;
         }
+        conf->reshape_checkpoint = jiffies;
         md_wakeup_thread(mddev->sync_thread);
         md_new_event(mddev);
         return 0;
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index cdd045681720..52ba99954dec 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -352,6 +352,8 @@ struct raid5_private_data {
         int                     previous_raid_disks;
         int                     prev_chunk, prev_algo;
         short                   generation; /* increments with every reshape */
+        unsigned long           reshape_checkpoint; /* Time we last updated
+                                                     * metadata */
 
         struct list_head        handle_list; /* stripes needing handling */
         struct list_head        hold_list; /* preread ready stripes */