1 files changed, 251 insertions, 158 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 7401540086df..08312b46463a 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -49,11 +49,26 @@ struct pending_exception {
         struct bio_list snapshot_bios;
 
         /*
-         * Other pending_exceptions that are processing this
-         * chunk.  When this list is empty, we know we can
-         * complete the origins.
+         * Short-term queue of pending exceptions prior to submission.
          */
-        struct list_head siblings;
+        struct list_head list;
+
+        /*
+         * The primary pending_exception is the one that holds
+         * the sibling_count and the list of origin_bios for a
+         * group of pending_exceptions.  It is always last to get freed.
+         * These fields get set up when writing to the origin.
+         */
+        struct pending_exception *primary_pe;
+
+        /*
+         * Number of pending_exceptions processing this chunk.
+         * When this drops to zero we must complete the origin bios.
+         * If incrementing or decrementing this, hold pe->snap->lock for
+         * the sibling concerned and not pe->primary_pe->snap->lock unless
+         * they are the same.
+         */
+        atomic_t sibling_count;
 
         /* Pointer back to snapshot context */
         struct dm_snapshot *snap;
@@ -377,6 +392,8 @@ static void read_snapshot_metadata(struct dm_snapshot *s)
                 down_write(&s->lock);
                 s->valid = 0;
                 up_write(&s->lock);
+
+                dm_table_event(s->table);
         }
 }
 
@@ -542,8 +559,12 @@ static void snapshot_dtr(struct dm_target *ti)
 {
         struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
 
+        /* Prevent further origin writes from using this snapshot. */
+        /* After this returns there can be no new kcopyd jobs. */
         unregister_snapshot(s);
 
+        kcopyd_client_destroy(s->kcopyd_client);
+
         exit_exception_table(&s->pending, pending_cache);
         exit_exception_table(&s->complete, exception_cache);
 
@@ -552,7 +573,7 @@ static void snapshot_dtr(struct dm_target *ti)
 
         dm_put_device(ti, s->origin);
         dm_put_device(ti, s->cow);
-        kcopyd_client_destroy(s->kcopyd_client);
+
         kfree(s);
 }
 
@@ -586,78 +607,117 @@ static void error_bios(struct bio *bio)
         }
 }
 
+static inline void error_snapshot_bios(struct pending_exception *pe)
+{
+        error_bios(bio_list_get(&pe->snapshot_bios));
+}
+
 static struct bio *__flush_bios(struct pending_exception *pe)
 {
-        struct pending_exception *sibling;
+        /*
+         * If this pe is involved in a write to the origin and
+         * it is the last sibling to complete then release
+         * the bios for the original write to the origin.
+         */
+
+        if (pe->primary_pe &&
+            atomic_dec_and_test(&pe->primary_pe->sibling_count))
+                return bio_list_get(&pe->primary_pe->origin_bios);
+
+        return NULL;
+}
+
+static void __invalidate_snapshot(struct dm_snapshot *s,
+                                struct pending_exception *pe, int err)
+{
+        if (!s->valid)
+                return;
 
-        if (list_empty(&pe->siblings))
-                return bio_list_get(&pe->origin_bios);
+        if (err == -EIO)
+                DMERR("Invalidating snapshot: Error reading/writing.");
+        else if (err == -ENOMEM)
+                DMERR("Invalidating snapshot: Unable to allocate exception.");
 
-        sibling = list_entry(pe->siblings.next,
-                             struct pending_exception, siblings);
+        if (pe)
+                remove_exception(&pe->e);
 
-        list_del(&pe->siblings);
+        if (s->store.drop_snapshot)
+                s->store.drop_snapshot(&s->store);
 
-        /* This is fine as long as kcopyd is single-threaded. If kcopyd
-         * becomes multi-threaded, we'll need some locking here.
-         */
-        bio_list_merge(&sibling->origin_bios, &pe->origin_bios);
+        s->valid = 0;
 
-        return NULL;
+        dm_table_event(s->table);
 }
 
 static void pending_complete(struct pending_exception *pe, int success)
 {
         struct exception *e;
+        struct pending_exception *primary_pe;
         struct dm_snapshot *s = pe->snap;
         struct bio *flush = NULL;
 
-        if (success) {
-                e = alloc_exception();
-                if (!e) {
-                        DMWARN("Unable to allocate exception.");
-                        down_write(&s->lock);
-                        s->store.drop_snapshot(&s->store);
-                        s->valid = 0;
-                        flush = __flush_bios(pe);
-                        up_write(&s->lock);
-
-                        error_bios(bio_list_get(&pe->snapshot_bios));
-                        goto out;
-                }
-                *e = pe->e;
-
-                /*
-                 * Add a proper exception, and remove the
-                 * in-flight exception from the list.
-                 */
+        if (!success) {
+                /* Read/write error - snapshot is unusable */
                 down_write(&s->lock);
-                insert_exception(&s->complete, e);
-                remove_exception(&pe->e);
+                __invalidate_snapshot(s, pe, -EIO);
                 flush = __flush_bios(pe);
-
-                /* Submit any pending write bios */
                 up_write(&s->lock);
 
-                flush_bios(bio_list_get(&pe->snapshot_bios));
-        } else {
-                /* Read/write error - snapshot is unusable */
+                error_snapshot_bios(pe);
+                goto out;
+        }
+
+        e = alloc_exception();
+        if (!e) {
                 down_write(&s->lock);
-                if (s->valid)
-                        DMERR("Error reading/writing snapshot");
-                s->store.drop_snapshot(&s->store);
-                s->valid = 0;
-                remove_exception(&pe->e);
+                __invalidate_snapshot(s, pe, -ENOMEM);
                 flush = __flush_bios(pe);
                 up_write(&s->lock);
 
-                error_bios(bio_list_get(&pe->snapshot_bios));
+                error_snapshot_bios(pe);
+                goto out;
+        }
+        *e = pe->e;
 
-                dm_table_event(s->table);
+        /*
+         * Add a proper exception, and remove the
+         * in-flight exception from the list.
+         */
+        down_write(&s->lock);
+        if (!s->valid) {
+                flush = __flush_bios(pe);
+                up_write(&s->lock);
+
+                free_exception(e);
+
+                error_snapshot_bios(pe);
+                goto out;
         }
 
+        insert_exception(&s->complete, e);
+        remove_exception(&pe->e);
+        flush = __flush_bios(pe);
+
+        up_write(&s->lock);
+
+        /* Submit any pending write bios */
+        flush_bios(bio_list_get(&pe->snapshot_bios));
+
  out:
-        free_pending_exception(pe);
+        primary_pe = pe->primary_pe;
+
+        /*
+         * Free the pe if it's not linked to an origin write or if
+         * it's not itself a primary pe.
+         */
+        if (!primary_pe || primary_pe != pe)
+                free_pending_exception(pe);
+
+        /*
+         * Free the primary pe if nothing references it.
+         */
+        if (primary_pe && !atomic_read(&primary_pe->sibling_count))
+                free_pending_exception(primary_pe);
 
         if (flush)
                 flush_bios(flush);
@@ -734,38 +794,45 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
         if (e) {
                 /* cast the exception to a pending exception */
                 pe = container_of(e, struct pending_exception, e);
+                goto out;
+        }
 
-        } else {
-                /*
-                 * Create a new pending exception, we don't want
-                 * to hold the lock while we do this.
-                 */
-                up_write(&s->lock);
-                pe = alloc_pending_exception();
-                down_write(&s->lock);
+        /*
+         * Create a new pending exception, we don't want
+         * to hold the lock while we do this.
+         */
+        up_write(&s->lock);
+        pe = alloc_pending_exception();
+        down_write(&s->lock);
 
-                e = lookup_exception(&s->pending, chunk);
-                if (e) {
-                        free_pending_exception(pe);
-                        pe = container_of(e, struct pending_exception, e);
-                } else {
-                        pe->e.old_chunk = chunk;
-                        bio_list_init(&pe->origin_bios);
-                        bio_list_init(&pe->snapshot_bios);
-                        INIT_LIST_HEAD(&pe->siblings);
-                        pe->snap = s;
-                        pe->started = 0;
-
-                        if (s->store.prepare_exception(&s->store, &pe->e)) {
-                                free_pending_exception(pe);
-                                s->valid = 0;
-                                return NULL;
-                        }
+        if (!s->valid) {
+                free_pending_exception(pe);
+                return NULL;
+        }
 
-                        insert_exception(&s->pending, &pe->e);
-                }
+        e = lookup_exception(&s->pending, chunk);
+        if (e) {
+                free_pending_exception(pe);
+                pe = container_of(e, struct pending_exception, e);
+                goto out;
+        }
+
+        pe->e.old_chunk = chunk;
+        bio_list_init(&pe->origin_bios);
+        bio_list_init(&pe->snapshot_bios);
+        pe->primary_pe = NULL;
+        atomic_set(&pe->sibling_count, 1);
+        pe->snap = s;
+        pe->started = 0;
+
+        if (s->store.prepare_exception(&s->store, &pe->e)) {
+                free_pending_exception(pe);
+                return NULL;
         }
 
+        insert_exception(&s->pending, &pe->e);
+
+ out:
         return pe;
 }
 
@@ -782,13 +849,15 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
 {
         struct exception *e;
         struct dm_snapshot *s = (struct dm_snapshot *) ti->private;
+        int copy_needed = 0;
         int r = 1;
         chunk_t chunk;
-        struct pending_exception *pe;
+        struct pending_exception *pe = NULL;
 
         chunk = sector_to_chunk(s, bio->bi_sector);
 
         /* Full snapshots are not usable */
+        /* To get here the table must be live so s->active is always set. */
         if (!s->valid)
                 return -EIO;
 
@@ -806,36 +875,41 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
                  * to copy an exception */
                 down_write(&s->lock);
 
+                if (!s->valid) {
+                        r = -EIO;
+                        goto out_unlock;
+                }
+
                 /* If the block is already remapped - use that, else remap it */
                 e = lookup_exception(&s->complete, chunk);
                 if (e) {
                         remap_exception(s, e, bio);
-                        up_write(&s->lock);
-
-                } else {
-                        pe = __find_pending_exception(s, bio);
-
-                        if (!pe) {
-                                if (s->store.drop_snapshot)
-                                        s->store.drop_snapshot(&s->store);
-                                s->valid = 0;
-                                r = -EIO;
-                                up_write(&s->lock);
-                        } else {
-                                remap_exception(s, &pe->e, bio);
-                                bio_list_add(&pe->snapshot_bios, bio);
-
-                                if (!pe->started) {
-                                        /* this is protected by snap->lock */
-                                        pe->started = 1;
-                                        up_write(&s->lock);
-                                        start_copy(pe);
-                                } else
-                                        up_write(&s->lock);
-                                r = 0;
-                        }
+                        goto out_unlock;
+                }
+
+                pe = __find_pending_exception(s, bio);
+                if (!pe) {
+                        __invalidate_snapshot(s, pe, -ENOMEM);
+                        r = -EIO;
+                        goto out_unlock;
+                }
+
+                remap_exception(s, &pe->e, bio);
+                bio_list_add(&pe->snapshot_bios, bio);
+
+                if (!pe->started) {
+                        /* this is protected by snap->lock */
+                        pe->started = 1;
+                        copy_needed = 1;
                 }
 
+                r = 0;
+
+ out_unlock:
+                up_write(&s->lock);
+
+                if (copy_needed)
+                        start_copy(pe);
         } else {
                 /*
                  * FIXME: this read path scares me because we
@@ -847,6 +921,11 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
                 /* Do reads */
                 down_read(&s->lock);
 
+                if (!s->valid) {
+                        up_read(&s->lock);
+                        return -EIO;
+                }
+
                 /* See if it it has been remapped */
                 e = lookup_exception(&s->complete, chunk);
                 if (e)
@@ -884,9 +963,9 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
                                 snap->store.fraction_full(&snap->store,
                                                           &numerator,
                                                           &denominator);
-                                snprintf(result, maxlen,
-                                         SECTOR_FORMAT "/" SECTOR_FORMAT,
-                                         numerator, denominator);
+                                snprintf(result, maxlen, "%llu/%llu",
+                                        (unsigned long long)numerator,
+                                        (unsigned long long)denominator);
                         }
                         else
                                 snprintf(result, maxlen, "Unknown");
@@ -899,9 +978,10 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
                  * to make private copies if the output is to
                  * make sense.
                  */
-                snprintf(result, maxlen, "%s %s %c " SECTOR_FORMAT,
+                snprintf(result, maxlen, "%s %s %c %llu",
                          snap->origin->name, snap->cow->name,
-                         snap->type, snap->chunk_size);
+                         snap->type,
+                         (unsigned long long)snap->chunk_size);
                 break;
         }
 
@@ -911,40 +991,27 @@ static int snapshot_status(struct dm_target *ti, status_type_t type,
 /*-----------------------------------------------------------------
  * Origin methods
  *---------------------------------------------------------------*/
-static void list_merge(struct list_head *l1, struct list_head *l2)
-{
-        struct list_head *l1_n, *l2_p;
-
-        l1_n = l1->next;
-        l2_p = l2->prev;
-
-        l1->next = l2;
-        l2->prev = l1;
-
-        l2_p->next = l1_n;
-        l1_n->prev = l2_p;
-}
-
 static int __origin_write(struct list_head *snapshots, struct bio *bio)
 {
-        int r = 1, first = 1;
+        int r = 1, first = 0;
         struct dm_snapshot *snap;
         struct exception *e;
-        struct pending_exception *pe, *last = NULL;
+        struct pending_exception *pe, *next_pe, *primary_pe = NULL;
         chunk_t chunk;
+        LIST_HEAD(pe_queue);
 
         /* Do all the snapshots on this origin */
         list_for_each_entry (snap, snapshots, list) {
 
+                down_write(&snap->lock);
+
                 /* Only deal with valid and active snapshots */
                 if (!snap->valid || !snap->active)
-                        continue;
+                        goto next_snapshot;
 
                 /* Nothing to do if writing beyond end of snapshot */
                 if (bio->bi_sector >= dm_table_get_size(snap->table))
-                        continue;
-
-                down_write(&snap->lock);
+                        goto next_snapshot;
 
                 /*
                  * Remember, different snapshots can have
@@ -956,49 +1023,75 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
                  * Check exception table to see if block
                  * is already remapped in this snapshot
                  * and trigger an exception if not.
+                 *
+                 * sibling_count is initialised to 1 so pending_complete()
+                 * won't destroy the primary_pe while we're inside this loop.
                  */
                 e = lookup_exception(&snap->complete, chunk);
-                if (!e) {
-                        pe = __find_pending_exception(snap, bio);
-                        if (!pe) {
-                                snap->store.drop_snapshot(&snap->store);
-                                snap->valid = 0;
-
-                        } else {
-                                if (last)
-                                        list_merge(&pe->siblings,
-                                                   &last->siblings);
-
-                                last = pe;
-                                r = 0;
+                if (e)
+                        goto next_snapshot;
+
+                pe = __find_pending_exception(snap, bio);
+                if (!pe) {
+                        __invalidate_snapshot(snap, pe, ENOMEM);
+                        goto next_snapshot;
+                }
+
+                if (!primary_pe) {
+                        /*
+                         * Either every pe here has same
+                         * primary_pe or none has one yet.
+                         */
+                        if (pe->primary_pe)
+                                primary_pe = pe->primary_pe;
+                        else {
+                                primary_pe = pe;
+                                first = 1;
                         }
+
+                        bio_list_add(&primary_pe->origin_bios, bio);
+
+                        r = 0;
+                }
+
+                if (!pe->primary_pe) {
+                        atomic_inc(&primary_pe->sibling_count);
+                        pe->primary_pe = primary_pe;
+                }
+
+                if (!pe->started) {
+                        pe->started = 1;
+                        list_add_tail(&pe->list, &pe_queue);
                 }
 
+ next_snapshot:
                 up_write(&snap->lock);
         }
 
+        if (!primary_pe)
+                goto out;
+
         /*
-         * Now that we have a complete pe list we can start the copying.
+         * If this is the first time we're processing this chunk and
+         * sibling_count is now 1 it means all the pending exceptions
+         * got completed while we were in the loop above, so it falls to
+         * us here to remove the primary_pe and submit any origin_bios.
          */
-        if (last) {
-                pe = last;
-                do {
-                        down_write(&pe->snap->lock);
-                        if (first)
-                                bio_list_add(&pe->origin_bios, bio);
-                        if (!pe->started) {
-                                pe->started = 1;
-                                up_write(&pe->snap->lock);
-                                start_copy(pe);
-                        } else
-                                up_write(&pe->snap->lock);
-                        first = 0;
-                        pe = list_entry(pe->siblings.next,
-                                        struct pending_exception, siblings);
-
-                } while (pe != last);
+
+        if (first && atomic_dec_and_test(&primary_pe->sibling_count)) {
+                flush_bios(bio_list_get(&primary_pe->origin_bios));
+                free_pending_exception(primary_pe);
+                /* If we got here, pe_queue is necessarily empty. */
+                goto out;
         }
 
+        /*
+         * Now that we have a complete pe list we can start the copying.
+         */
+        list_for_each_entry_safe(pe, next_pe, &pe_queue, list)
+                start_copy(pe);
+
+ out:
         return r;
 }