From: NeilBrown <neilb@suse.de>
To: Shaohua Li <shli@kernel.org>
Cc: linux-raid@vger.kernel.org, djbw@fb.com
Subject: Re: [patch 3/3] raid5: relieve lock contention in get_active_stripe()
Date: Tue, 3 Sep 2013 16:08:58 +1000 [thread overview]
Message-ID: <20130903160858.2175a41b@notabene.brown> (raw)
In-Reply-To: <20130828063953.GD17163@kernel.org>
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On Wed, 28 Aug 2013 14:39:53 +0800 Shaohua Li <shli@kernel.org> wrote:
> On Wed, Aug 28, 2013 at 02:32:52PM +1000, NeilBrown wrote:
> > On Tue, 27 Aug 2013 16:53:30 +0800 Shaohua Li <shli@kernel.org> wrote:
> >
> > > On Tue, Aug 27, 2013 at 01:17:52PM +1000, NeilBrown wrote:
> >
> > >
> > > > Then get_active_stripe wouldn't need to worry about device_lock at all and
> > > > would only need to get the hash lock for the particular sector. That should
> > > > make it a lot simpler.
> > >
> > > did you mean get_active_stripe() doesn't need device_lock for any code path?
> > > How could it be safe? device_lock still protects something like handle_list,
> > > delayed_list, which release_stripe() will use while a get_active_stripe can run
> > > concurrently.
> >
> > Yes you will still need device_lock to protect list_del_init(&sh->lru),
> > as well as the hash lock.
> > Do you need device_lock anywhere else in there?
>
> That's what I mean. So I need get both device_lock and hash_lock. To not
> deadlock, I need release hash_lock and relock device_lock/hash_lock. Since I
> release lock, I need recheck if I can find the stripe in hash again. So the
> seqcount locking doesn't simplify things here. I thought the seqlock only fixes
> one race. Did I miss anything?
Can you order the locks so that you take the hash_lock first, then the
device_lock? That would be a lot simpler.
>
> I saw your tree only has seqcount_write lock in one place, but there are still
> other places which changing quiesce, degraded. I thought we still need lock all
> locks like what I did.
Can you be specific? I thought I had convinced my self that I covered
everything that was necessary, but I might have missed something.
NeilBrown
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next prev parent reply other threads:[~2013-09-03 6:08 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-12 2:24 [patch 0/3] raid5: relieve lock contention of get_active_stripe() Shaohua Li
2013-08-12 2:24 ` [patch 1/3] raid5: rename stripe_hash() Shaohua Li
2013-08-12 2:24 ` [patch 2/3] wait: add wait_event_cmd() Shaohua Li
2013-08-12 2:24 ` [patch 3/3] raid5: relieve lock contention in get_active_stripe() Shaohua Li
2013-08-27 3:17 ` NeilBrown
2013-08-27 8:53 ` Shaohua Li
2013-08-28 4:32 ` NeilBrown
2013-08-28 6:39 ` Shaohua Li
2013-09-03 6:08 ` NeilBrown [this message]
2013-09-03 7:02 ` Shaohua Li
2013-09-04 6:41 ` NeilBrown
2013-09-05 5:40 ` Shaohua Li
2013-09-05 6:29 ` NeilBrown
2013-09-05 9:18 ` Shaohua Li
2013-09-09 4:33 ` Shaohua Li
2013-09-10 1:13 ` NeilBrown
2013-09-10 2:35 ` Shaohua Li
2013-09-10 4:06 ` NeilBrown
2013-09-10 4:24 ` Shaohua Li
2013-09-10 5:20 ` NeilBrown
2013-09-10 6:59 ` Shaohua Li
2013-09-10 7:28 ` NeilBrown
2013-09-10 7:37 ` Shaohua Li
2013-09-11 1:34 ` NeilBrown
2013-09-12 1:55 ` Shaohua Li
2013-09-12 5:38 ` NeilBrown
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