md/raid5: fix 'out of memory' during raid cache recovery

This fixes the case when md array assembly fails because of raid cache recovery
unable to allocate a stripe, despite attempts to replay stripes and increase
cache size. This happens because stripes released by r5c_recovery_replay_stripes
and raid5_set_cache_size don't become available for allocation immediately.
Released stripes first are placed on conf->released_stripes list and require
md thread to merge them on conf->inactive_list before they can be allocated.

Patch allows final allocation attempt during cache recovery to wait for
new stripes to become availabe for allocation.

Cc: linux-raid@vger.kernel.org
Cc: Shaohua Li <shli@kernel.org>
Cc: linux-stable <stable@vger.kernel.org> # 4.10+
Fixes: b4c625c67362 ("md/r5cache: r5cache recovery: part 1")
Signed-off-by: Alexei Naberezhnov <anaberezhnov@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 4990f03..cecea90 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6369,6 +6369,7 @@ raid5_show_stripe_cache_size(struct mddev *mddev, char *page)
 int
 raid5_set_cache_size(struct mddev *mddev, int size)
 {
+	int result = 0;
 	struct r5conf *conf = mddev->private;
 
 	if (size <= 16 || size > 32768)
@@ -6385,11 +6386,14 @@ raid5_set_cache_size(struct mddev *mddev, int size)
 
 	mutex_lock(&conf->cache_size_mutex);
 	while (size > conf->max_nr_stripes)
-		if (!grow_one_stripe(conf, GFP_KERNEL))
+		if (!grow_one_stripe(conf, GFP_KERNEL)) {
+			conf->min_nr_stripes = conf->max_nr_stripes;
+			result = -ENOMEM;
 			break;
+		}
 	mutex_unlock(&conf->cache_size_mutex);
 
-	return 0;
+	return result;
 }
 EXPORT_SYMBOL(raid5_set_cache_size);