From: "J. Bruce Fields" <bfields@fieldses.org>
To: Neil Brown <neilb@suse.de>
Cc: linux-nfs@vger.kernel.org
Subject: Re: [PATCH 1.5/6] Fix race in new request delay code.
Date: Tue, 21 Sep 2010 22:15:18 -0400 [thread overview]
Message-ID: <20100922021518.GB22021@fieldses.org> (raw)
In-Reply-To: <20100921183521.4510af63@notabene>
On Tue, Sep 21, 2010 at 06:35:21PM +1000, Neil Brown wrote:
> On Mon, 30 Aug 2010 09:36:08 +1000
> Neil Brown <neilb@suse.de> wrote:
>
> > On Thu, 26 Aug 2010 17:08:00 -0400
> > "J. Bruce Fields" <bfields@fieldses.org> wrote:
> >
> > > On Tue, Aug 17, 2010 at 03:15:09PM +1000, NeilBrown wrote:
> > > > If the 'wait_for_completion_interruptible_timeout' completes due
> > > > to interrupt or timeout, just before cache_revisit request gets around
> > > > to calling ->revisit and thus the completion, we have a race with bad
> > > > consequences.
> > > >
> > > > cache_defer_req will see that sleeper.handle.hash is empty (because
> > > > cache_revisit_request has already done the list_del_init), and that
> > > > CACHE_PENDING is clear, and so will exit that function leaving any
> > > > local variables such as 'sleeper' undefined.
> > > >
> > > > Meanwhile cache_revisit_request could delete sleeper.handle.recent
> > > > from the 'pending' list, and call sleeper.hande.revisit, any of which
> > > > could have new garbage values and so could trigger a BUG.
> > >
> > > Thanks, this looks correct to me!
> > >
> > > I wish it were simpler, but don't see how right now.
> >
> > I think the way to make it simpler is to get rid of the deferral altogether.
> > The more I think about it the less I like it :-)
>
> I was in the process of doing this "getting rid of deferral" when I
> discovered that lockd now uses deferral too (and has done for 4 years! I am
> out of touch!!). This is for NFS exporting cluster filesystems where 'lock'
> might take a while, but returns a 'grant'.
>
> As lockd is single-threads we cannot just let it wait for the grant
> in-process.
>
> So I guess I cannot rip all that code out after all :-(
Yeah, I'd forgotten about that. Eventually perhaps we can fix lockd....
--b.
prev parent reply other threads:[~2010-09-22 2:16 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-12 7:04 [PATCH 0/6] Cache deferral improvements - try N+2 NeilBrown
2010-08-12 7:04 ` [PATCH 2/6] nfsd/idmap: drop special request deferal in favour of improved default NeilBrown
[not found] ` <20100812070406.11459.89468.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-09-21 21:08 ` J. Bruce Fields
2010-08-12 7:04 ` [PATCH 1/6] sunrpc/cache: allow threads to block while waiting for cache update NeilBrown
2010-08-12 7:04 ` [PATCH 3/6] sunrpc: close connection when a request is irretrievably lost NeilBrown
2010-09-21 20:53 ` J. Bruce Fields
2010-09-21 23:37 ` Neil Brown
2010-09-22 2:13 ` J. Bruce Fields
2010-08-12 7:04 ` [PATCH 5/6] svcauth_gss: replace a trivial 'switch' with an 'if' NeilBrown
2010-08-12 7:04 ` [PATCH 4/6] nfsd: disable deferral for NFSv4 NeilBrown
[not found] ` <20100812070407.11459.2929.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-09-21 21:01 ` J. Bruce Fields
2010-08-12 7:04 ` [PATCH 6/6] sunrpc/cache: change deferred-request hash table to use hlist NeilBrown
[not found] ` <20100812065722.11459.18978.stgit-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
2010-08-12 12:03 ` [PATCH 0/6] Cache deferral improvements - try N+2 J. Bruce Fields
2010-08-17 5:15 ` [PATCH 1.5/6] Fix race in new request delay code NeilBrown
2010-08-26 21:08 ` J. Bruce Fields
2010-08-29 23:36 ` Neil Brown
2010-09-01 11:31 ` J. Bruce Fields
2010-09-21 8:35 ` Neil Brown
2010-09-22 2:15 ` J. Bruce Fields [this message]
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