dm: keep old table until after resume succeeded

When swapping a new table into place, retain the old table until
its replacement is in place.

An old check for an empty table is removed because this is enforced
in populate_table().

__unbind() becomes redundant when followed by __bind().

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

2 files changed, 23 insertions, 21 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index a3d20265ffc1..63fd4de25bda 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -855,7 +855,7 @@ static int do_resume(struct dm_ioctl *param)
         unsigned suspend_flags = DM_SUSPEND_LOCKFS_FLAG;
         struct hash_cell *hc;
         struct mapped_device *md;
-        struct dm_table *new_map;
+        struct dm_table *new_map, *old_map = NULL;
 
         down_write(&_hash_lock);
 
@@ -884,11 +884,11 @@ static int do_resume(struct dm_ioctl *param)
                 if (!dm_suspended(md))
                         dm_suspend(md, suspend_flags);
 
-                r = dm_swap_table(md, new_map);
-                if (r) {
+                old_map = dm_swap_table(md, new_map);
+                if (IS_ERR(old_map)) {
                         dm_table_destroy(new_map);
                         dm_put(md);
-                        return r;
+                        return PTR_ERR(old_map);
                 }
 
                 if (dm_table_get_mode(new_map) & FMODE_WRITE)
@@ -900,6 +900,8 @@ static int do_resume(struct dm_ioctl *param)
         if (dm_suspended(md))
                 r = dm_resume(md);
 
+        if (old_map)
+                dm_table_destroy(old_map);
 
         if (!r) {
                 dm_kobject_uevent(md, KOBJ_CHANGE, param->event_nr);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 255b75c61544..c254c6cf69a1 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -2033,9 +2033,13 @@ static void __set_size(struct mapped_device *md, sector_t size)
         mutex_unlock(&md->bdev->bd_inode->i_mutex);
 }
 
-static int __bind(struct mapped_device *md, struct dm_table *t,
-                  struct queue_limits *limits)
+/*
+ * Returns old map, which caller must destroy.
+ */
+static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
+                               struct queue_limits *limits)
 {
+        struct dm_table *old_map;
         struct request_queue *q = md->queue;
         sector_t size;
         unsigned long flags;
@@ -2050,11 +2054,6 @@ static int __bind(struct mapped_device *md, struct dm_table *t,
 
         __set_size(md, size);
 
-        if (!size) {
-                dm_table_destroy(t);
-                return 0;
-        }
-
         dm_table_event_callback(t, event_callback, md);
 
         /*
@@ -2070,11 +2069,12 @@ static int __bind(struct mapped_device *md, struct dm_table *t,
         __bind_mempools(md, t);
 
         write_lock_irqsave(&md->map_lock, flags);
+        old_map = md->map;
         md->map = t;
         dm_table_set_restrictions(t, q, limits);
         write_unlock_irqrestore(&md->map_lock, flags);
 
-        return 0;
+        return old_map;
 }
 
 /*
@@ -2368,13 +2368,13 @@ static void dm_rq_barrier_work(struct work_struct *work)
 }
 
 /*
- * Swap in a new table (destroying old one).
+ * Swap in a new table, returning the old one for the caller to destroy.
  */
-int dm_swap_table(struct mapped_device *md, struct dm_table *table)
+struct dm_table *dm_swap_table(struct mapped_device *md, struct dm_table *table)
 {
-        struct dm_table *map;
+        struct dm_table *map = ERR_PTR(-EINVAL);
         struct queue_limits limits;
-        int r = -EINVAL;
+        int r;
 
         mutex_lock(&md->suspend_lock);
 
@@ -2383,8 +2383,10 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
                 goto out;
 
         r = dm_calculate_queue_limits(table, &limits);
-        if (r)
+        if (r) {
+                map = ERR_PTR(r);
                 goto out;
+        }
 
         /* cannot change the device type, once a table is bound */
         if (md->map &&
@@ -2393,13 +2395,11 @@ int dm_swap_table(struct mapped_device *md, struct dm_table *table)
                 goto out;
         }
 
-        map = __unbind(md);
-        r = __bind(md, table, &limits);
-        dm_table_destroy(map);
+        map = __bind(md, table, &limits);
 
 out:
         mutex_unlock(&md->suspend_lock);
-        return r;
+        return map;
 }
 
 /*