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-rw-r--r--drivers/md/dm-snap.c122
1 files changed, 80 insertions, 42 deletions
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 874f145431d..475514bda9d 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -54,11 +54,21 @@ struct pending_exception {
struct list_head list;
/*
- * Other pending_exceptions that are processing this
- * chunk. When this list is empty, we know we can
- * complete the origins.
+ * 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 list_head siblings;
+ 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;
@@ -593,20 +603,15 @@ static void error_bios(struct bio *bio)
static struct bio *__flush_bios(struct pending_exception *pe)
{
- struct pending_exception *sibling;
-
- if (list_empty(&pe->siblings))
- return bio_list_get(&pe->origin_bios);
-
- sibling = list_entry(pe->siblings.next,
- struct pending_exception, siblings);
-
- list_del(&pe->siblings);
-
- /* This is fine as long as kcopyd is single-threaded. If kcopyd
- * becomes multi-threaded, we'll need some locking here.
+ /*
+ * 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.
*/
- bio_list_merge(&sibling->origin_bios, &pe->origin_bios);
+
+ if (pe->primary_pe &&
+ atomic_dec_and_test(&pe->primary_pe->sibling_count))
+ return bio_list_get(&pe->primary_pe->origin_bios);
return NULL;
}
@@ -614,6 +619,7 @@ static struct bio *__flush_bios(struct pending_exception *pe)
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;
@@ -662,7 +668,20 @@ static void pending_complete(struct pending_exception *pe, int success)
}
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);
@@ -757,7 +776,8 @@ __find_pending_exception(struct dm_snapshot *s, struct bio *bio)
pe->e.old_chunk = chunk;
bio_list_init(&pe->origin_bios);
bio_list_init(&pe->snapshot_bios);
- INIT_LIST_HEAD(&pe->siblings);
+ pe->primary_pe = NULL;
+ atomic_set(&pe->sibling_count, 1);
pe->snap = s;
pe->started = 0;
@@ -916,26 +936,12 @@ 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, *next_pe, *last = NULL;
+ struct pending_exception *pe, *next_pe, *primary_pe = NULL;
chunk_t chunk;
LIST_HEAD(pe_queue);
@@ -962,6 +968,9 @@ 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) {
@@ -971,31 +980,60 @@ static int __origin_write(struct list_head *snapshots, struct bio *bio)
snap->valid = 0;
} else {
- if (first) {
- bio_list_add(&pe->origin_bios, bio);
+ 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;
- first = 0;
}
- if (last && list_empty(&pe->siblings))
- list_merge(&pe->siblings,
- &last->siblings);
+ 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);
}
- last = pe;
}
}
up_write(&snap->lock);
}
+ if (!primary_pe)
+ goto out;
+
+ /*
+ * 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 (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;
}