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[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>
This commit is contained in:
Alasdair G Kergon 2006-10-03 01:15:30 -07:00 committed by Linus Torvalds
parent ca3a931fd3
commit 4b832e8de2
1 changed files with 48 additions and 35 deletions
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83
drivers/md/dm-snap.c
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@ -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;
}