linux-kernel - Re: 2.6.19-rc6-mm2

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Date:	Fri, 8 Dec 2006 12:31:41 +1100
From:	Neil Brown <neilb@...e.de>
To:	Jiri Kosina <jikos@...os.cz>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.19-rc6-mm2

On Tuesday December 5, jikos@...os.cz wrote:
> On Tue, 5 Dec 2006, Jiri Kosina wrote:
> 
> > It seemed to be 100% reproducible - happened on every boot of FC6 
> > system, so it was probably triggered by some raid/lvm command executed 
> > from init scripts after boot, but I didn't examine it further. As soon 
> > as I get to the machine where this happens, I will try to narrow it down 
> > to the exact userspace command that triggers it and will let you know 
> > (probably this evening).
> 
> OK, so more details follow (I am not sure how valuable they are, though). 

They do help a bit..

I've found a possible race that could possibly be related to this
BUG.  Can you try this patch and see if it helps?

Note: this isn't the final form I would use to fix the race, but if it
makes a difference, then it tells me I am on the right track.

Thanks,
NeilBrown


Signed-off-by: Neil Brown <neilb@...e.de>

### Diffstat output
 ./drivers/md/md.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff .prev/drivers/md/md.c ./drivers/md/md.c
--- .prev/drivers/md/md.c	2006-12-06 14:49:20.000000000 +1100
+++ ./drivers/md/md.c	2006-12-07 10:29:40.000000000 +1100
@@ -222,10 +222,14 @@ static inline mddev_t *mddev_get(mddev_t
 	return mddev;
 }
 
+static DEFINE_MUTEX(disks_mutex);
 static void mddev_put(mddev_t *mddev)
 {
-	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
+	mutex_lock(&disks_mutex);
+	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock)) {
+		mutex_unlock(&disks_mutex);
 		return;
+	}
 	list_del(&mddev->all_mddevs);
 	spin_unlock(&all_mddevs_lock);
 
@@ -234,6 +238,7 @@ static void mddev_put(mddev_t *mddev)
 	blk_cleanup_queue(mddev->queue);
 	mddev->queue = NULL;
 	kobject_unregister(&mddev->kobj);
+	mutex_unlock(&disks_mutex);
 }
 
 static mddev_t * mddev_find(dev_t unit)
@@ -2948,7 +2953,6 @@ int mdp_major = 0;
 
 static struct kobject *md_probe(dev_t dev, int *part, void *data)
 {
-	static DEFINE_MUTEX(disks_mutex);
 	mddev_t *mddev = mddev_find(dev);
 	struct gendisk *disk;
 	int partitioned = (MAJOR(dev) != MD_MAJOR);
-
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