1 files changed, 71 insertions, 4 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index f972a94bbc32..d4b233c25f2e 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -366,6 +366,73 @@ static struct stripe_head *__find_stripe(raid5_conf_t *conf, sector_t sector,
         return NULL;
 }
 
+/*
+ * Need to check if array has failed when deciding whether to:
+ *  - start an array
+ *  - remove non-faulty devices
+ *  - add a spare
+ *  - allow a reshape
+ * This determination is simple when no reshape is happening.
+ * However if there is a reshape, we need to carefully check
+ * both the before and after sections.
+ * This is because some failed devices may only affect one
+ * of the two sections, and some non-in_sync devices may
+ * be insync in the section most affected by failed devices.
+ */
+static int has_failed(raid5_conf_t *conf)
+{
+        int degraded;
+        int i;
+        if (conf->mddev->reshape_position == MaxSector)
+                return conf->mddev->degraded > conf->max_degraded;
+
+        rcu_read_lock();
+        degraded = 0;
+        for (i = 0; i < conf->previous_raid_disks; i++) {
+                mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
+                if (!rdev || test_bit(Faulty, &rdev->flags))
+                        degraded++;
+                else if (test_bit(In_sync, &rdev->flags))
+                        ;
+                else
+                        /* not in-sync or faulty.
+                         * If the reshape increases the number of devices,
+                         * this is being recovered by the reshape, so
+                         * this 'previous' section is not in_sync.
+                         * If the number of devices is being reduced however,
+                         * the device can only be part of the array if
+                         * we are reverting a reshape, so this section will
+                         * be in-sync.
+                         */
+                        if (conf->raid_disks >= conf->previous_raid_disks)
+                                degraded++;
+        }
+        rcu_read_unlock();
+        if (degraded > conf->max_degraded)
+                return 1;
+        rcu_read_lock();
+        degraded = 0;
+        for (i = 0; i < conf->raid_disks; i++) {
+                mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
+                if (!rdev || test_bit(Faulty, &rdev->flags))
+                        degraded++;
+                else if (test_bit(In_sync, &rdev->flags))
+                        ;
+                else
+                        /* not in-sync or faulty.
+                         * If reshape increases the number of devices, this
+                         * section has already been recovered, else it
+                         * almost certainly hasn't.
+                         */
+                        if (conf->raid_disks <= conf->previous_raid_disks)
+                                degraded++;
+        }
+        rcu_read_unlock();
+        if (degraded > conf->max_degraded)
+                return 1;
+        return 0;
+}
+
 static void unplug_slaves(mddev_t *mddev);
 static void raid5_unplug_device(struct request_queue *q);
 
@@ -5006,7 +5073,7 @@ static int run(mddev_t *mddev)
         mddev->degraded = (max(conf->raid_disks, conf->previous_raid_disks)
                            - working_disks);
 
-        if (mddev->degraded > conf->max_degraded) {
+        if (has_failed(conf)) {
                 printk(KERN_ERR "md/raid:%s: not enough operational devices"
                         " (%d/%d failed)\n",
                         mdname(mddev), mddev->degraded, conf->raid_disks);
@@ -5244,7 +5311,7 @@ static int raid5_remove_disk(mddev_t *mddev, int number)
                  * isn't possible.
                  */
                 if (!test_bit(Faulty, &rdev->flags) &&
-                    mddev->degraded <= conf->max_degraded &&
+                    !has_failed(conf) &&
                     number < conf->raid_disks) {
                         err = -EBUSY;
                         goto abort;
@@ -5272,7 +5339,7 @@ static int raid5_add_disk(mddev_t *mddev, mdk_rdev_t *rdev)
         int first = 0;
         int last = conf->raid_disks - 1;
 
-        if (mddev->degraded > conf->max_degraded)
+        if (has_failed(conf))
                 /* no point adding a device */
                 return -EINVAL;
 
@@ -5364,7 +5431,7 @@ static int check_reshape(mddev_t *mddev)
         if (mddev->bitmap)
                 /* Cannot grow a bitmap yet */
                 return -EBUSY;
-        if (mddev->degraded > conf->max_degraded)
+        if (has_failed(conf))
                 return -EINVAL;
         if (mddev->delta_disks < 0) {
                 /* We might be able to shrink, but the devices must