2 files changed, 39 insertions, 4 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e57213dacd25..295be1a68806 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -74,6 +74,8 @@ static DEFINE_SPINLOCK(pers_lock);
 
 static void md_print_devices(void);
 
+static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
+
 #define MD_BUG(x...) { printk("md: bug in file %s, line %d\n", __FILE__, __LINE__); md_print_devices(); }
 
 /*
@@ -3013,6 +3015,36 @@ degraded_show(mddev_t *mddev, char *page)
 static struct md_sysfs_entry md_degraded = __ATTR_RO(degraded);
 
 static ssize_t
+sync_force_parallel_show(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%d\n", mddev->parallel_resync);
+}
+
+static ssize_t
+sync_force_parallel_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        long n;
+
+        if (strict_strtol(buf, 10, &n))
+                return -EINVAL;
+
+        if (n != 0 && n != 1)
+                return -EINVAL;
+
+        mddev->parallel_resync = n;
+
+        if (mddev->sync_thread)
+                wake_up(&resync_wait);
+
+        return len;
+}
+
+/* force parallel resync, even with shared block devices */
+static struct md_sysfs_entry md_sync_force_parallel =
+__ATTR(sync_force_parallel, S_IRUGO|S_IWUSR,
+       sync_force_parallel_show, sync_force_parallel_store);
+
+static ssize_t
 sync_speed_show(mddev_t *mddev, char *page)
 {
         unsigned long resync, dt, db;
@@ -3187,6 +3219,7 @@ static struct attribute *md_redundancy_attrs[] = {
         &md_sync_min.attr,
         &md_sync_max.attr,
         &md_sync_speed.attr,
+        &md_sync_force_parallel.attr,
         &md_sync_completed.attr,
         &md_max_sync.attr,
         &md_suspend_lo.attr,
@@ -5487,8 +5520,6 @@ void md_allow_write(mddev_t *mddev)
 }
 EXPORT_SYMBOL_GPL(md_allow_write);
 
-static DECLARE_WAIT_QUEUE_HEAD(resync_wait);
-
 #define SYNC_MARKS      10
 #define SYNC_MARK_STEP  (3*HZ)
 void md_do_sync(mddev_t *mddev)
@@ -5552,8 +5583,9 @@ void md_do_sync(mddev_t *mddev)
                 for_each_mddev(mddev2, tmp) {
                         if (mddev2 == mddev)
                                 continue;
-                        if (mddev2->curr_resync && 
-                            match_mddev_units(mddev,mddev2)) {
+                        if (!mddev->parallel_resync
+                        &&  mddev2->curr_resync
+                        &&  match_mddev_units(mddev, mddev2)) {
                                 DEFINE_WAIT(wq);
                                 if (mddev < mddev2 && mddev->curr_resync == 2) {
                                         /* arbitrarily yield */
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 812ffa590cff..a6d7ab688ede 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -180,6 +180,9 @@ struct mddev_s
         int                             sync_speed_min;
         int                             sync_speed_max;
 
+        /* resync even though the same disks are shared among md-devices */
+        int                             parallel_resync;
+
         int                             ok_start_degraded;
         /* recovery/resync flags 
          * NEEDED:   we might need to start a resync/recover