[PATCH] dm snapshot: tidy pe ref counting

Rename sibling_count to ref_count and introduce get and put functions.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 48 insertions, 35 deletions

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 1c6485404db4..638c8d90da0e 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -59,7 +59,7 @@ struct pending_exception {
 
         /*
          * The primary pending_exception is the one that holds
-         * the sibling_count and the list of origin_bios for a
+         * the ref_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.
          */
@@ -72,7 +72,7 @@ struct pending_exception {
          * the sibling concerned and not pe->primary_pe->snap->lock unless
          * they are the same.
          */
-        atomic_t sibling_count;
+        atomic_t ref_count;
 
         /* Pointer back to snapshot context */
         struct dm_snapshot *snap;
@@ -653,10 +653,46 @@ static void __invalidate_snapshot(struct dm_snapshot *s,
         dm_table_event(s->table);
 }
 
+static void get_pending_exception(struct pending_exception *pe)
+{
+        atomic_inc(&pe->ref_count);
+}
+
+static struct bio *put_pending_exception(struct pending_exception *pe)
+{
+        struct pending_exception *primary_pe;
+        struct bio *origin_bios = NULL;
+
+        primary_pe = pe->primary_pe;
+
+        /*
+         * 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 (primary_pe &&
+            atomic_dec_and_test(&primary_pe->ref_count))
+                origin_bios = bio_list_get(&primary_pe->origin_bios);
+
+        /*
+         * 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->ref_count))
+                free_pending_exception(primary_pe);
+
+        return origin_bios;
+}
+
 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 *origin_bios = NULL;
         struct bio *snapshot_bios = NULL;
@@ -695,30 +731,7 @@ static void pending_complete(struct pending_exception *pe, int success)
 
  out:
         snapshot_bios = bio_list_get(&pe->snapshot_bios);
-
-        primary_pe = pe->primary_pe;
-
-        /*
-         * 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 (primary_pe &&
-            atomic_dec_and_test(&primary_pe->sibling_count))
-                origin_bios = bio_list_get(&primary_pe->origin_bios);
-
-        /*
-         * 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);
+        origin_bios = put_pending_exception(pe);
 
         up_write(&s->lock);
 
@@ -829,7 +842,7 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
         bio_list_init(&pe->origin_bios);
         bio_list_init(&pe->snapshot_bios);
         pe->primary_pe = NULL;
-        atomic_set(&pe->sibling_count, 1);
+        atomic_set(&pe->ref_count, 0);
         pe->snap = s;
         pe->started = 0;
 
@@ -838,6 +851,7 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
                 return NULL;
         }
 
+        get_pending_exception(pe);
         insert_exception(&s->pending, &pe->e);
 
  out:
@@ -1012,7 +1026,7 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
                  * is already remapped in this snapshot
                  * and trigger an exception if not.
                  *
-                 * sibling_count is initialised to 1 so pending_complete()
+                 * ref_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);
@@ -1043,8 +1057,8 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
                 }
 
                 if (!pe->primary_pe) {
-                        atomic_inc(&primary_pe->sibling_count);
                         pe->primary_pe = primary_pe;
+                        get_pending_exception(primary_pe);
                 }
 
                 if (!pe->started) {
@@ -1057,20 +1071,20 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
         }
 
         if (!primary_pe)
-                goto out;
+                return r;
 
         /*
          * If this is the first time we're processing this chunk and
-         * sibling_count is now 1 it means all the pending exceptions
+         * ref_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 (first && atomic_dec_and_test(&primary_pe->sibling_count)) {
+        if (first && atomic_dec_and_test(&primary_pe->ref_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;
+                return r;
         }
 
         /*
@@ -1079,7 +1093,6 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
         list_for_each_entry_safe(pe, next_pe, &pe_queue, list)
                 start_copy(pe);
 
- out:
         return r;
 }