dm thin: allow pool in read-only mode to transition to read-write mode

A thin-pool may be in read-only mode because the pool's data or metadata
space was exhausted.  To allow for recovery, by adding more space to the
pool, we must allow a pool to transition from PM_READ_ONLY to PM_WRITE
mode.  Otherwise, running out of space will render the pool permanently
read-only.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 0d7852e2b275..ee29037ffc2e 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1425,6 +1425,7 @@ static void set_pool_mode(struct pool *pool, enum pool_mode mode)
                 break;
 
         case PM_WRITE:
+                dm_pool_metadata_read_write(pool->pmd);
                 pool->process_bio = process_bio;
                 pool->process_discard = process_discard;
                 pool->process_prepared_mapping = process_prepared_mapping;
@@ -1641,12 +1642,19 @@ static int bind_control_target(struct pool *pool, struct dm_target *ti)
         struct pool_c *pt = ti->private;
 
         /*
-         * We want to make sure that degraded pools are never upgraded.
+         * We want to make sure that a pool in PM_FAIL mode is never upgraded.
          */
         enum pool_mode old_mode = pool->pf.mode;
         enum pool_mode new_mode = pt->adjusted_pf.mode;
 
-        if (old_mode > new_mode)
+        /*
+         * If we were in PM_FAIL mode, rollback of metadata failed.  We're
+         * not going to recover without a thin_repair.  So we never let the
+         * pool move out of the old mode.  On the other hand a PM_READ_ONLY
+         * may have been due to a lack of metadata or data space, and may
+         * now work (ie. if the underlying devices have been resized).
+         */
+        if (old_mode == PM_FAIL)
                 new_mode = old_mode;
 
         pool->ti = ti;