3 files changed, 50 insertions, 1 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 77b90ae66991..100368eb7991 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1212,6 +1212,41 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
         return &t->targets[(KEYS_PER_NODE * n) + k];
 }
 
+static int count_device(struct dm_target *ti, struct dm_dev *dev,
+                        sector_t start, sector_t len, void *data)
+{
+        unsigned *num_devices = data;
+
+        (*num_devices)++;
+
+        return 0;
+}
+
+/*
+ * Check whether a table has no data devices attached using each
+ * target's iterate_devices method.
+ * Returns false if the result is unknown because a target doesn't
+ * support iterate_devices.
+ */
+bool dm_table_has_no_data_devices(struct dm_table *table)
+{
+        struct dm_target *uninitialized_var(ti);
+        unsigned i = 0, num_devices = 0;
+
+        while (i < dm_table_get_num_targets(table)) {
+                ti = dm_table_get_target(table, i++);
+
+                if (!ti->type->iterate_devices)
+                        return false;
+
+                ti->type->iterate_devices(ti, count_device, &num_devices);
+                if (num_devices)
+                        return false;
+        }
+
+        return true;
+}
+
 /*
  * Establish the new table's queue_limits and validate them.
  */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 6748e0c4df1f..67ffa391edcf 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2429,7 +2429,7 @@ static void dm_queue_flush(struct mapped_device *md)
  */
 struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
 {
-        struct dm_table *map = ERR_PTR(-EINVAL);
+        struct dm_table *live_map, *map = ERR_PTR(-EINVAL);
         struct queue_limits limits;
         int r;
 
@@ -2439,6 +2439,19 @@ struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
         if (!dm_suspended_md(md))
                 goto out;
 
+        /*
+         * If the new table has no data devices, retain the existing limits.
+         * This helps multipath with queue_if_no_path if all paths disappear,
+         * then new I/O is queued based on these limits, and then some paths
+         * reappear.
+         */
+        if (dm_table_has_no_data_devices(table)) {
+                live_map = dm_get_live_table(md);
+                if (live_map)
+                        limits = md->queue->limits;
+                dm_table_put(live_map);
+        }
+
         r = dm_calculate_queue_limits(table, &limits);
         if (r) {
                 map = ERR_PTR(r);
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index 52eef493d266..6a99fefaa743 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -54,6 +54,7 @@ void dm_table_event_callback(struct dm_table *t,
                              void (*fn)(void *), void *context);
 struct dm_target *dm_table_get_target(struct dm_table *t, unsigned int index);
 struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector);
+bool dm_table_has_no_data_devices(struct dm_table *table);
 int dm_calculate_queue_limits(struct dm_table *table,
                               struct queue_limits *limits);
 void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,