Commit 4b832e8d authored by Alasdair G Kergon's avatar Alasdair G Kergon Committed by Linus Torvalds
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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: default avatarAlasdair G Kergon <agk@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent ca3a931f

drivers/md/dm-snap.c

+48 −35
Original line number Diff line number Diff line
@@ -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;

}