commit 8b9cd157dc030924afaeb1dd1a4d3306f5bda118
Author: Maksymilian Kunt <maksymilian.kunt@intel.com>
Date:   Mon Nov 13 12:30:49 2017 +0100

    imsm: continue resync on 3-disk RAID10
    
    If RAID10 gets degraded during resync and is stopped, it doesn't continue
    resync after automatic assemble and it is reported to be in sync. Resync
    is blocked because the disk is missing. It should not happen for RAID10 as
    it can still continue with 3 disks.
    
    Count missing disks. Block resync only if number of missing disks exceeds
    limit for given RAID level (only different for RAID10). Check if the
    disk under recovery is present. If not, resync should be allowed to run.
    
    Signed-off-by: Maksymilian Kunt <maksymilian.kunt@intel.com>
    Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
    Signed-off-by: Jes Sorensen <jsorensen@fb.com>

diff --git a/super-intel.c b/super-intel.c
index 2f912f2..c55802f 100644
--- a/super-intel.c
+++ b/super-intel.c
@@ -1342,6 +1342,20 @@ static unsigned long long round_size_to_mb(unsigned long long size, unsigned int
 	return size;
 }
 
+static int able_to_resync(int raid_level, int missing_disks)
+{
+	int max_missing_disks = 0;
+
+	switch (raid_level) {
+	case 10:
+		max_missing_disks = 1;
+		break;
+	default:
+		max_missing_disks = 0;
+	}
+	return missing_disks <= max_missing_disks;
+}
+
 /* try to determine how much space is reserved for metadata from
  * the last get_extents() entry on the smallest active disk,
  * otherwise fallback to the default
@@ -7645,6 +7659,7 @@ static struct mdinfo *container_content_imsm(struct supertype *st, char *subarra
 		int slot;
 		int chunk;
 		char *ep;
+		int level;
 
 		if (subarray &&
 		    (i != strtoul(subarray, &ep, 10) || *ep != '\0'))
@@ -7653,6 +7668,7 @@ static struct mdinfo *container_content_imsm(struct supertype *st, char *subarra
 		dev = get_imsm_dev(super, i);
 		map = get_imsm_map(dev, MAP_0);
 		map2 = get_imsm_map(dev, MAP_1);
+		level = get_imsm_raid_level(map);
 
 		/* do not publish arrays that are in the middle of an
 		 * unsupported migration
@@ -7675,8 +7691,8 @@ static struct mdinfo *container_content_imsm(struct supertype *st, char *subarra
 		chunk = __le16_to_cpu(map->blocks_per_strip) >> 1;
 		/* mdadm does not support all metadata features- set the bit in all arrays state */
 		if (!validate_geometry_imsm_orom(super,
-						 get_imsm_raid_level(map), /* RAID level */
-						 imsm_level_to_layout(get_imsm_raid_level(map)),
+						 level, /* RAID level */
+						 imsm_level_to_layout(level),
 						 map->num_members, /* raid disks */
 						 &chunk, join_u32(dev->size_low, dev->size_high),
 						 1 /* verbose */)) {
@@ -7700,6 +7716,7 @@ static struct mdinfo *container_content_imsm(struct supertype *st, char *subarra
 			int idx;
 			int skip;
 			__u32 ord;
+			int missing = 0;
 
 			skip = 0;
 			idx = get_imsm_disk_idx(dev, slot, MAP_0);
@@ -7713,19 +7730,27 @@ static struct mdinfo *container_content_imsm(struct supertype *st, char *subarra
 				skip = 1;
 			if (d && is_failed(&d->disk))
 				skip = 1;
-			if (ord & IMSM_ORD_REBUILD)
+			if (!skip && (ord & IMSM_ORD_REBUILD))
 				recovery_start = 0;
 
 			/*
 			 * if we skip some disks the array will be assmebled degraded;
 			 * reset resync start to avoid a dirty-degraded
 			 * situation when performing the intial sync
-			 *
-			 * FIXME handle dirty degraded
 			 */
-			if ((skip || recovery_start == 0) &&
-			    !(dev->vol.dirty & RAIDVOL_DIRTY))
-				this->resync_start = MaxSector;
+			if (skip)
+				missing++;
+
+			if (!(dev->vol.dirty & RAIDVOL_DIRTY)) {
+				if ((!able_to_resync(level, missing) ||
+				     recovery_start == 0))
+					this->resync_start = MaxSector;
+			} else {
+				/*
+				 * FIXME handle dirty degraded
+				 */
+			}
+
 			if (skip)
 				continue;