1 files changed, 67 insertions, 3 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index ae5fd0b9c75c..28fc282b61b2 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -232,6 +232,13 @@ struct thin_c {
         struct bio_list deferred_bio_list;
         struct bio_list retry_on_resume_list;
         struct rb_root sort_bio_list; /* sorted list of deferred bios */
+
+        /*
+         * Ensures the thin is not destroyed until the worker has finished
+         * iterating the active_thins list.
+         */
+        atomic_t refcount;
+        struct completion can_destroy;
 };
 
 /*----------------------------------------------------------------*/
@@ -1486,6 +1493,45 @@ static void process_thin_deferred_bios(struct thin_c *tc)
         blk_finish_plug(&plug);
 }
 
+static void thin_get(struct thin_c *tc);
+static void thin_put(struct thin_c *tc);
+
+/*
+ * We can't hold rcu_read_lock() around code that can block.  So we
+ * find a thin with the rcu lock held; bump a refcount; then drop
+ * the lock.
+ */
+static struct thin_c *get_first_thin(struct pool *pool)
+{
+        struct thin_c *tc = NULL;
+
+        rcu_read_lock();
+        if (!list_empty(&pool->active_thins)) {
+                tc = list_entry_rcu(pool->active_thins.next, struct thin_c, list);
+                thin_get(tc);
+        }
+        rcu_read_unlock();
+
+        return tc;
+}
+
+static struct thin_c *get_next_thin(struct pool *pool, struct thin_c *tc)
+{
+        struct thin_c *old_tc = tc;
+
+        rcu_read_lock();
+        list_for_each_entry_continue_rcu(tc, &pool->active_thins, list) {
+                thin_get(tc);
+                thin_put(old_tc);
+                rcu_read_unlock();
+                return tc;
+        }
+        thin_put(old_tc);
+        rcu_read_unlock();
+
+        return NULL;
+}
+
 static void process_deferred_bios(struct pool *pool)
 {
         unsigned long flags;
@@ -1493,10 +1539,11 @@ static void process_deferred_bios(struct pool *pool)
         struct bio_list bios;
         struct thin_c *tc;
 
-        rcu_read_lock();
-        list_for_each_entry_rcu(tc, &pool->active_thins, list)
+        tc = get_first_thin(pool);
+        while (tc) {
                 process_thin_deferred_bios(tc);
-        rcu_read_unlock();
+                tc = get_next_thin(pool, tc);
+        }
 
         /*
          * If there are any deferred flush bios, we must commit
@@ -3061,11 +3108,25 @@ static struct target_type pool_target = {
 /*----------------------------------------------------------------
  * Thin target methods
  *--------------------------------------------------------------*/
+static void thin_get(struct thin_c *tc)
+{
+        atomic_inc(&tc->refcount);
+}
+
+static void thin_put(struct thin_c *tc)
+{
+        if (atomic_dec_and_test(&tc->refcount))
+                complete(&tc->can_destroy);
+}
+
 static void thin_dtr(struct dm_target *ti)
 {
         struct thin_c *tc = ti->private;
         unsigned long flags;
 
+        thin_put(tc);
+        wait_for_completion(&tc->can_destroy);
+
         spin_lock_irqsave(&tc->pool->lock, flags);
         list_del_rcu(&tc->list);
         spin_unlock_irqrestore(&tc->pool->lock, flags);
@@ -3192,6 +3253,9 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
 
         mutex_unlock(&dm_thin_pool_table.mutex);
 
+        atomic_set(&tc->refcount, 1);
+        init_completion(&tc->can_destroy);
+
         spin_lock_irqsave(&tc->pool->lock, flags);
         list_add_tail_rcu(&tc->list, &tc->pool->active_thins);
         spin_unlock_irqrestore(&tc->pool->lock, flags);