dm clone metadata: Use a two phase commit

Split the metadata commit in two parts:

1. dm_clone_metadata_pre_commit(): Prepare the current transaction for
   committing. After this is called, all subsequent metadata updates,
   done through either dm_clone_set_region_hydrated() or
   dm_clone_cond_set_range(), will be part of the next transaction.

2. dm_clone_metadata_commit(): Actually commit the current transaction
   to disk and start a new transaction.

This is required by the following commit. It allows dm-clone to flush
the destination device after step (1) to ensure that all freshly
hydrated regions, for which we are updating the metadata, are properly
written to non-volatile storage and won't be lost in case of a crash.

Fixes: 7431b7835f55 ("dm: add clone target")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-clone-metadata.c b/drivers/md/dm-clone-metadata.c
index ee870a425ab8b2f2e68b86685602ef4eb1796a1c..c05b121104561a4cd777b40cdb97ba14838f7ff2 100644 (file)
--- a/drivers/md/dm-clone-metadata.c
+++ b/drivers/md/dm-clone-metadata.c
@@ -127,6 +127,9 @@ struct dm_clone_metadata {
        struct dirty_map dmap[2];
        struct dirty_map *current_dmap;
 
+       /* Protected by lock */
+       struct dirty_map *committing_dmap;
+
        /*
         * In core copy of the on-disk bitmap to save constantly doing look ups
         * on disk.
@@ -511,6 +514,7 @@ static int dirty_map_init(struct dm_clone_metadata *cmd)
        }
 
        cmd->current_dmap = &cmd->dmap[0];
+       cmd->committing_dmap = NULL;
 
        return 0;
 }
@@ -775,15 +779,17 @@ static int __flush_dmap(struct dm_clone_metadata *cmd, struct dirty_map *dmap)
        return 0;
 }
 
-int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
+int dm_clone_metadata_pre_commit(struct dm_clone_metadata *cmd)
 {
-       int r = -EPERM;
+       int r = 0;
        struct dirty_map *dmap, *next_dmap;
 
        down_write(&cmd->lock);
 
-       if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+       if (cmd->fail_io || dm_bm_is_read_only(cmd->bm)) {
+               r = -EPERM;
                goto out;
+       }
 
        /* Get current dirty bitmap */
        dmap = cmd->current_dmap;
@@ -795,7 +801,7 @@ int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
         * The last commit failed, so we don't have a clean dirty-bitmap to
         * use.
         */
-       if (WARN_ON(next_dmap->changed)) {
+       if (WARN_ON(next_dmap->changed || cmd->committing_dmap)) {
                r = -EINVAL;
                goto out;
        }
@@ -805,11 +811,33 @@ int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
        cmd->current_dmap = next_dmap;
        spin_unlock_irq(&cmd->bitmap_lock);
 
-       /*
-        * No one is accessing the old dirty bitmap anymore, so we can flush
-        * it.
-        */
-       r = __flush_dmap(cmd, dmap);
+       /* Set old dirty bitmap as currently committing */
+       cmd->committing_dmap = dmap;
+out:
+       up_write(&cmd->lock);
+
+       return r;
+}
+
+int dm_clone_metadata_commit(struct dm_clone_metadata *cmd)
+{
+       int r = -EPERM;
+
+       down_write(&cmd->lock);
+
+       if (cmd->fail_io || dm_bm_is_read_only(cmd->bm))
+               goto out;
+
+       if (WARN_ON(!cmd->committing_dmap)) {
+               r = -EINVAL;
+               goto out;
+       }
+
+       r = __flush_dmap(cmd, cmd->committing_dmap);
+       if (!r) {
+               /* Clear committing dmap */
+               cmd->committing_dmap = NULL;
+       }
 out:
        up_write(&cmd->lock);
 

diff --git a/drivers/md/dm-clone-metadata.h b/drivers/md/dm-clone-metadata.h
index 3fe50a781c1161a1050707331fa2c28169a8a917..14af1ebd853fd2048acc445e0c8b8e8a978b28c5 100644 (file)
--- a/drivers/md/dm-clone-metadata.h
+++ b/drivers/md/dm-clone-metadata.h
@@ -75,7 +75,23 @@ void dm_clone_metadata_close(struct dm_clone_metadata *cmd);
 
 /*
  * Commit dm-clone metadata to disk.
+ *
+ * We use a two phase commit:
+ *
+ * 1. dm_clone_metadata_pre_commit(): Prepare the current transaction for
+ *    committing. After this is called, all subsequent metadata updates, done
+ *    through either dm_clone_set_region_hydrated() or
+ *    dm_clone_cond_set_range(), will be part of the **next** transaction.
+ *
+ * 2. dm_clone_metadata_commit(): Actually commit the current transaction to
+ *    disk and start a new transaction.
+ *
+ * This allows dm-clone to flush the destination device after step (1) to
+ * ensure that all freshly hydrated regions, for which we are updating the
+ * metadata, are properly written to non-volatile storage and won't be lost in
+ * case of a crash.
  */
+int dm_clone_metadata_pre_commit(struct dm_clone_metadata *cmd);
 int dm_clone_metadata_commit(struct dm_clone_metadata *cmd);
 
 /*
@@ -112,6 +128,7 @@ int dm_clone_metadata_abort(struct dm_clone_metadata *cmd);
  * Switches metadata to a read only mode. Once read-only mode has been entered
  * the following functions will return -EPERM:
  *
+ *   dm_clone_metadata_pre_commit()
  *   dm_clone_metadata_commit()
  *   dm_clone_set_region_hydrated()
  *   dm_clone_cond_set_range()

diff --git a/drivers/md/dm-clone-target.c b/drivers/md/dm-clone-target.c
index b3d89072d21c6a26461dd9a60d32eaccf68200a5..613c913c296c7e3c63f9949ef85ebb96d915c00e 100644 (file)
--- a/drivers/md/dm-clone-target.c
+++ b/drivers/md/dm-clone-target.c
@@ -1122,8 +1122,13 @@ static int commit_metadata(struct clone *clone)
                goto out;
        }
 
-       r = dm_clone_metadata_commit(clone->cmd);
+       r = dm_clone_metadata_pre_commit(clone->cmd);
+       if (unlikely(r)) {
+               __metadata_operation_failed(clone, "dm_clone_metadata_pre_commit", r);
+               goto out;
+       }
 
+       r = dm_clone_metadata_commit(clone->cmd);
        if (unlikely(r)) {
                __metadata_operation_failed(clone, "dm_clone_metadata_commit", r);
                goto out;