1 files changed, 36 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 */