[dm-devel] Calltrace in dm-snapshot in 2.6.27 kernel

[Mikulas Patocka]

On Wed, 22 Oct 2008, aluno3 at poczta.onet.pl wrote:

> Hi
> 
> I used your patch and I ran test the same workload. After a few hours
> test, everything is OK. Is it possible? Test is still running.When I get
> something wrong from kernel I write to You again.

Hi

That's good that it works. So try this. Keep the first patch (it is this 
one --- 
http://people.redhat.com/mpatocka/patches/kernel/2.6.27/dm-snapshot-fix-primary-pe-race.patch 
--- I think Milan already sent it to you and you have it applied). Undo 
the second patch (that one that hides deallocation with /* */ ). And apply 
this. Run the same test.

Mikulas

---
 drivers/md/dm-snap.c |   10 +++++++++-
 drivers/md/dm-snap.h |    2 ++
 2 files changed, 11 insertions(+), 1 deletion(-)

Index: linux-2.6.27-clean/drivers/md/dm-snap.c
===================================================================
--- linux-2.6.27-clean.orig/drivers/md/dm-snap.c	2008-10-22 15:41:24.000000000 +0200
+++ linux-2.6.27-clean/drivers/md/dm-snap.c	2008-10-22 15:51:33.000000000 +0200
@@ -368,6 +368,7 @@ static struct dm_snap_pending_exception 
 	struct dm_snap_pending_exception *pe = mempool_alloc(s->pending_pool,
 							     GFP_NOIO);
 
+	atomic_inc(&s->n_pending_exceptions);
 	pe->snap = s;
 
 	return pe;
@@ -375,7 +376,10 @@ static struct dm_snap_pending_exception 
 
 static void free_pending_exception(struct dm_snap_pending_exception *pe)
 {
-	mempool_free(pe, pe->snap->pending_pool);
+	struct struct dm_snapshot *s = pe->snap;
+	mempool_free(pe, s->pending_pool);
+	smp_mb__before_atomic_dec();
+	atomic_dec(&s->n_pending_exceptions);
 }
 
 static void insert_completed_exception(struct dm_snapshot *s,
@@ -601,6 +605,7 @@ static int snapshot_ctr(struct dm_target
 	s->valid = 1;
 	s->active = 0;
 	s->last_percent = 0;
+	atomic_set(&s->n_pending_exceptions, 0);
 	init_rwsem(&s->lock);
 	spin_lock_init(&s->pe_lock);
 	s->ti = ti;
@@ -727,6 +732,9 @@ static void snapshot_dtr(struct dm_targe
 	/* After this returns there can be no new kcopyd jobs. */
 	unregister_snapshot(s);
 
+	while (atomic_read(&s->n_pending_exceptions))
+		yield();
+
 #ifdef CONFIG_DM_DEBUG
 	for (i = 0; i < DM_TRACKED_CHUNK_HASH_SIZE; i++)
 		BUG_ON(!hlist_empty(&s->tracked_chunk_hash[i]));
Index: linux-2.6.27-clean/drivers/md/dm-snap.h
===================================================================
--- linux-2.6.27-clean.orig/drivers/md/dm-snap.h	2008-10-22 15:45:08.000000000 +0200
+++ linux-2.6.27-clean/drivers/md/dm-snap.h	2008-10-22 15:46:49.000000000 +0200
@@ -163,6 +163,8 @@ struct dm_snapshot {
 
 	mempool_t *pending_pool;
 
+	atomic_t n_pending_exceptions;
+
 	struct exception_table pending;
 	struct exception_table complete;