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Date: Sat, 6 Mar 2004 14:40:18 +0100
From: Miquel van Smoorenburg <miquels@cistron.nl>
To: Andrew Morton <akpm@osdl.org>
Cc: Joe Thornber <thornber@redhat.com>
Subject: Re: [PATCH] dm-rwlock.patch (Re: 2.6.4-rc1-mm1: queue-congestion-dm-implementation patch)
Message-ID: <20040306134018.GA13030@cistron.nl>
References: <cistron.200403011400.51008.kevcorry@us.ibm.com> <20040302130137.GA9941@cistron.nl> <200403020826.52448.kevcorry@us.ibm.com> <20040303211624.GA11008@cistron.nl> <20040305135544.318de1a6.akpm@osdl.org>
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According to Andrew Morton:
> Miquel van Smoorenburg <miquels@cistron.nl> wrote:
> >
> > I posted a patch in the wrong thread earlier today, and the patch also
> > wasn't so good. This should be better, but I'll let Joe be the
> > judge of that. At least it survived my testing.
>
> Joe just sent me a dm update which broke your patch big-time.
>
> I've dropped a snapshot of my tree at
> http://www.zipworld.com.au/~akpm/linux/patches/stuff/x.gz (against rc2).
> Would you have time to update and retest the rwlock patch?
Sure. I'm taking a new approach, since the rwlock patch was still
not correct - sleeping functions could still be called under
the rwlock, for example dm-crypt does that in its mapping function.
Fixing that would get way too complicated. So:
dm-maplock.patch
This patch adds a rwlock_t maplock to the struct mapped_device.
The ->map member is only updated with that lock held. dm_any_congested
takes the lock, and so can be sure that the table under ->map won't change.
This patch is much smaller and simpler than dm-rwlock.patch.
--- linux-2.6.4-rc2-mmX.orig/drivers/md/dm.c 2004-03-06 04:00:02.000000000 +0100
+++ linux-2.6.4-rc2-mmX/drivers/md/dm.c 2004-03-06 13:24:20.000000000 +0100
@@ -49,6 +49,7 @@
struct mapped_device {
struct rw_semaphore lock;
+ rwlock_t maplock;
atomic_t holders;
unsigned long flags;
@@ -564,9 +565,12 @@
int r;
struct mapped_device *md = congested_data;
- down_read(&md->lock);
- r = dm_table_any_congested(md->map, bdi_bits);
- up_read(&md->lock);
+ read_lock(&md->maplock);
+ if (md->map == NULL || test_bit(DMF_BLOCK_IO, &md->flags))
+ r = bdi_bits;
+ else
+ r = dm_table_any_congested(md->map, bdi_bits);
+ read_unlock(&md->maplock);
return r;
}
@@ -642,6 +646,7 @@
memset(md, 0, sizeof(*md));
init_rwsem(&md->lock);
+ rwlock_init(&md->maplock);
atomic_set(&md->holders, 1);
md->queue = blk_alloc_queue(GFP_KERNEL);
@@ -741,7 +746,9 @@
if (size == 0)
return 0;
+ write_lock(&md->maplock);
md->map = t;
+ write_unlock(&md->maplock);
dm_table_event_callback(md->map, event_callback, md);
dm_table_get(t);
@@ -751,12 +758,16 @@
static void __unbind(struct mapped_device *md)
{
- if (!md->map)
+ struct dm_table *map = md->map;
+
+ if (!map)
return;
- dm_table_event_callback(md->map, NULL, NULL);
- dm_table_put(md->map);
+ dm_table_event_callback(map, NULL, NULL);
+ write_lock(&md->maplock);
md->map = NULL;
+ write_unlock(&md->maplock);
+ dm_table_put(map);
}
/*