2 files changed, 58 insertions, 8 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6f97817d28b9..34b6902cda46 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1558,15 +1558,30 @@ static void md_print_devices(void)
 }
 
 
-static void sync_sbs(mddev_t * mddev)
+static void sync_sbs(mddev_t * mddev, int nospares)
 {
+        /* Update each superblock (in-memory image), but
+         * if we are allowed to, skip spares which already
+         * have the right event counter, or have one earlier
+         * (which would mean they aren't being marked as dirty
+         * with the rest of the array)
+         */
         mdk_rdev_t *rdev;
         struct list_head *tmp;
 
         ITERATE_RDEV(mddev,rdev,tmp) {
-                super_types[mddev->major_version].
-                        sync_super(mddev, rdev);
-                rdev->sb_loaded = 1;
+                if (rdev->sb_events == mddev->events ||
+                    (nospares &&
+                     rdev->raid_disk < 0 &&
+                     (rdev->sb_events&1)==0 &&
+                     rdev->sb_events+1 == mddev->events)) {
+                        /* Don't update this superblock */
+                        rdev->sb_loaded = 2;
+                } else {
+                        super_types[mddev->major_version].
+                                sync_super(mddev, rdev);
+                        rdev->sb_loaded = 1;
+                }
         }
 }
 
@@ -1576,12 +1591,42 @@ void md_update_sb(mddev_t * mddev)
         struct list_head *tmp;
         mdk_rdev_t *rdev;
         int sync_req;
+        int nospares = 0;
 
 repeat:
         spin_lock_irq(&mddev->write_lock);
         sync_req = mddev->in_sync;
         mddev->utime = get_seconds();
-        mddev->events ++;
+        if (mddev->sb_dirty == 3)
+                /* just a clean<-> dirty transition, possibly leave spares alone,
+                 * though if events isn't the right even/odd, we will have to do
+                 * spares after all
+                 */
+                nospares = 1;
+
+        /* If this is just a dirty<->clean transition, and the array is clean
+         * and 'events' is odd, we can roll back to the previous clean state */
+        if (mddev->sb_dirty == 3
+            && (mddev->in_sync && mddev->recovery_cp == MaxSector)
+            && (mddev->events & 1))
+                mddev->events--;
+        else {
+                /* otherwise we have to go forward and ... */
+                mddev->events ++;
+                if (!mddev->in_sync || mddev->recovery_cp != MaxSector) { /* not clean */
+                        /* .. if the array isn't clean, insist on an odd 'events' */
+                        if ((mddev->events&1)==0) {
+                                mddev->events++;
+                                nospares = 0;
+                        }
+                } else {
+                        /* otherwise insist on an even 'events' (for clean states) */
+                        if ((mddev->events&1)) {
+                                mddev->events++;
+                                nospares = 0;
+                        }
+                }
+        }
 
         if (!mddev->events) {
                 /*
@@ -1593,7 +1638,7 @@ repeat:
                 mddev->events --;
         }
         mddev->sb_dirty = 2;
-        sync_sbs(mddev);
+        sync_sbs(mddev, nospares);
 
         /*
          * do not write anything to disk if using
@@ -1615,6 +1660,8 @@ repeat:
         ITERATE_RDEV(mddev,rdev,tmp) {
                 char b[BDEVNAME_SIZE];
                 dprintk(KERN_INFO "md: ");
+                if (rdev->sb_loaded != 1)
+                        continue; /* no noise on spare devices */
                 if (test_bit(Faulty, &rdev->flags))
                         dprintk("(skipping faulty ");
 
@@ -1626,6 +1673,7 @@ repeat:
                         dprintk(KERN_INFO "(write) %s's sb offset: %llu\n",
                                 bdevname(rdev->bdev,b),
                                 (unsigned long long)rdev->sb_offset);
+                        rdev->sb_events = mddev->events;
 
                 } else
                         dprintk(")\n");
@@ -1895,6 +1943,7 @@ static mdk_rdev_t *md_import_device(dev_t newdev, int super_format, int super_mi
         rdev->desc_nr = -1;
         rdev->flags = 0;
         rdev->data_offset = 0;
+        rdev->sb_events = 0;
         atomic_set(&rdev->nr_pending, 0);
         atomic_set(&rdev->read_errors, 0);
         atomic_set(&rdev->corrected_errors, 0);
@@ -4708,7 +4757,7 @@ void md_write_start(mddev_t *mddev, struct bio *bi)
                 spin_lock_irq(&mddev->write_lock);
                 if (mddev->in_sync) {
                         mddev->in_sync = 0;
-                        mddev->sb_dirty = 1;
+                        mddev->sb_dirty = 3;
                         md_wakeup_thread(mddev->thread);
                 }
                 spin_unlock_irq(&mddev->write_lock);
@@ -5055,7 +5104,7 @@ void md_check_recovery(mddev_t *mddev)
                 if (mddev->safemode && !atomic_read(&mddev->writes_pending) &&
                     !mddev->in_sync && mddev->recovery_cp == MaxSector) {
                         mddev->in_sync = 1;
-                        mddev->sb_dirty = 1;
+                        mddev->sb_dirty = 3;
                 }
                 if (mddev->safemode == 1)
                         mddev->safemode = 0;
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 682574f3bd36..c1e0ac55bab5 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -58,6 +58,7 @@ struct mdk_rdev_s
 
         struct page     *sb_page;
         int             sb_loaded;
+        __u64           sb_events;
         sector_t        data_offset;    /* start of data in array */
         sector_t        sb_offset;
         int             sb_size;        /* bytes in the superblock */