1 files changed, 55 insertions, 0 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3086da5664f3..0ff5469c03d2 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -972,10 +972,61 @@ void dm_accept_partial_bio(struct bio *bio, unsigned n_sectors)
 }
 EXPORT_SYMBOL_GPL(dm_accept_partial_bio);
 
+/*
+ * Flush current->bio_list when the target map method blocks.
+ * This fixes deadlocks in snapshot and possibly in other targets.
+ */
+struct dm_offload {
+        struct blk_plug plug;
+        struct blk_plug_cb cb;
+};
+
+static void flush_current_bio_list(struct blk_plug_cb *cb, bool from_schedule)
+{
+        struct dm_offload *o = container_of(cb, struct dm_offload, cb);
+        struct bio_list list;
+        struct bio *bio;
+
+        INIT_LIST_HEAD(&o->cb.list);
+
+        if (unlikely(!current->bio_list))
+                return;
+
+        list = *current->bio_list;
+        bio_list_init(current->bio_list);
+
+        while ((bio = bio_list_pop(&list))) {
+                struct bio_set *bs = bio->bi_pool;
+                if (unlikely(!bs) || bs == fs_bio_set) {
+                        bio_list_add(current->bio_list, bio);
+                        continue;
+                }
+
+                spin_lock(&bs->rescue_lock);
+                bio_list_add(&bs->rescue_list, bio);
+                queue_work(bs->rescue_workqueue, &bs->rescue_work);
+                spin_unlock(&bs->rescue_lock);
+        }
+}
+
+static void dm_offload_start(struct dm_offload *o)
+{
+        blk_start_plug(&o->plug);
+        o->cb.callback = flush_current_bio_list;
+        list_add(&o->cb.list, &current->plug->cb_list);
+}
+
+static void dm_offload_end(struct dm_offload *o)
+{
+        list_del(&o->cb.list);
+        blk_finish_plug(&o->plug);
+}
+
 static void __map_bio(struct dm_target_io *tio)
 {
         int r;
         sector_t sector;
+        struct dm_offload o;
         struct bio *clone = &tio->clone;
         struct dm_target *ti = tio->ti;
 
@@ -988,7 +1039,11 @@ static void __map_bio(struct dm_target_io *tio)
          */
         atomic_inc(&tio->io->io_count);
         sector = clone->bi_iter.bi_sector;
+
+        dm_offload_start(&o);
         r = ti->type->map(ti, clone);
+        dm_offload_end(&o);
+
         if (r == DM_MAPIO_REMAPPED) {
                 /* the bio has been remapped so dispatch it */