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Re: [dm-devel] [PATCH] 2.6.12-rc6: fix rh_dec()/rh_inc() race in dm-raid1.c



could this be solved by doing your patch in rh_dec and just moving the atomic_inc in rh_inc? The reason I ask is that the mark_region log call can block.

 brassow
On Jun 16, 2005, at 5:51 PM, Jun'ichi Nomura wrote:

Hello,

Attached patch fixes the another bug in dm-raid1.c that
the dirty region may stay in or be moved to clean list
and freed while in use.

It happens as follows:

CPU0 CPU1
----------------------------------------------------------------------- -------
rh_dec()
if (atomic_dec_and_test(pending))
<the region is still marked dirty>
rh_inc()
if the region is clean
mark the region dirty
and remove from clean list
mark the region clean
and move to clean list
atomic_inc(pending)


At this stage, the region is in clean list and
will be mistakenly reclaimed by rh_update_states() later.

Signed-off-by: Jun'ichi Nomura <j-nomura ce jp nec com>

--- kernel/drivers/md/dm-raid1.c.orig 2005-06-16 07:13:50.610325768 -0400
+++ kernel/drivers/md/dm-raid1.c 2005-06-16 10:34:12.510719112 -0400
@@ -375,16 +380,18 @@ static void rh_inc(struct region_hash *r


 	read_lock(&rh->hash_lock);
 	reg = __rh_find(rh, region);
+
+	atomic_inc(&reg->pending);
+
+	spin_lock_irq(&rh->region_lock);
 	if (reg->state == RH_CLEAN) {
 		rh->log->type->mark_region(rh->log, reg->key);

-		spin_lock_irq(&rh->region_lock);
 		reg->state = RH_DIRTY;
 		list_del_init(&reg->list);	/* take off the clean list */
-		spin_unlock_irq(&rh->region_lock);
 	}
+	spin_unlock_irq(&rh->region_lock);

-	atomic_inc(&reg->pending);
 	read_unlock(&rh->hash_lock);
 }

@@ -408,6 +414,10 @@ static void rh_dec(struct region_hash *r

 	if (atomic_dec_and_test(&reg->pending)) {
 		spin_lock_irqsave(&rh->region_lock, flags);
+		if (atomic_read(&reg->pending)) { /* check race */
+			spin_unlock_irqrestore(&rh->region_lock, flags);
+			return;
+		}
 		if (reg->state == RH_RECOVERING) {
 			list_add_tail(&reg->list, &rh->quiesced_regions);
 		} else {
--
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