1 files changed, 28 insertions, 2 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index bb4b733697b3..4c80e82f941c 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -71,7 +71,10 @@ struct dm_snapshot {
         /* List of snapshots per Origin */
         struct list_head list;
 
-        /* You can't use a snapshot if this is 0 (e.g. if full) */
+        /*
+         * You can't use a snapshot if this is 0 (e.g. if full).
+         * A snapshot-merge target never clears this.
+         */
         int valid;
 
         /* Origin writes don't trigger exceptions until this is set */
@@ -107,6 +110,21 @@ struct dm_snapshot {
         spinlock_t tracked_chunk_lock;
         struct hlist_head tracked_chunk_hash[DM_TRACKED_CHUNK_HASH_SIZE];
 
+        /*
+         * The merge operation failed if this flag is set.
+         * Failure modes are handled as follows:
+         * - I/O error reading the header
+         *      => don't load the target; abort.
+         * - Header does not have "valid" flag set
+         *      => use the origin; forget about the snapshot.
+         * - I/O error when reading exceptions
+         *      => don't load the target; abort.
+         *         (We can't use the intermediate origin state.)
+         * - I/O error while merging
+         *      => stop merging; set merge_failed; process I/O normally.
+         */
+        int merge_failed;
+
         /* Wait for events based on state_bits */
         unsigned long state_bits;
 
@@ -900,9 +918,13 @@ static void snapshot_merge_next_chunks(struct dm_snapshot *s)
         linear_chunks = s->store->type->prepare_merge(s->store, &old_chunk,
                                                       &new_chunk);
         if (linear_chunks <= 0) {
-                if (linear_chunks < 0)
+                if (linear_chunks < 0) {
                         DMERR("Read error in exception store: "
                               "shutting down merge");
+                        down_write(&s->lock);
+                        s->merge_failed = 1;
+                        up_write(&s->lock);
+                }
                 goto shut;
         }
 
@@ -988,6 +1010,7 @@ static void merge_callback(int read_err, unsigned long write_err, void *context)
 
 shut:
         down_write(&s->lock);
+        s->merge_failed = 1;
         b = __release_queued_bios_after_merge(s);
         up_write(&s->lock);
         error_bios(b);
@@ -1090,6 +1113,7 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
         INIT_LIST_HEAD(&s->list);
         spin_lock_init(&s->pe_lock);
         s->state_bits = 0;
+        s->merge_failed = 0;
         s->first_merging_chunk = 0;
         s->num_merging_chunks = 0;
         bio_list_init(&s->bios_queued_during_merge);
@@ -1835,6 +1859,8 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 
                 if (!snap->valid)
                         DMEMIT("Invalid");
+                else if (snap->merge_failed)
+                        DMEMIT("Merge failed");
                 else {
                         if (snap->store->type->usage) {
                                 sector_t total_sectors, sectors_allocated,