linux-kernel - Re: [PATCH 3/4] sunrpc: make rpc_wait_bit

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Message-ID: <20111011091404.208a03b5@tlielax.poochiereds.net>
Date:	Tue, 11 Oct 2011 09:14:04 -0400
From:	Jeff Layton <jlayton@...hat.com>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
Cc:	"Pavel Machek" <pavel@....cz>, <smfrench@...il.com>, <rjw@...k.pl>,
	<linux-pm@...ts.linux-foundation.org>,
	<linux-cifs@...r.kernel.org>, <linux-nfs@...r.kernel.org>,
	<john@...va.COM>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] sunrpc: make rpc_wait_bit_killable handle freeze
 events

On Tue, 11 Oct 2011 05:52:57 -0700
"Myklebust, Trond" <Trond.Myklebust@...app.com> wrote:

> > -----Original Message-----
> > From: Jeff Layton [mailto:jlayton@...hat.com]
> > Sent: Tuesday, October 11, 2011 6:12 AM
> > To: Pavel Machek
> > Cc: Myklebust, Trond; smfrench@...il.com; rjw@...k.pl; linux-
> > pm@...ts.linux-foundation.org; linux-cifs@...r.kernel.org; linux-
> > nfs@...r.kernel.org; john@...va.COM; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH 3/4] sunrpc: make rpc_wait_bit_killable handle
> freeze
> > events
> > 
> > On Tue, 11 Oct 2011 08:19:23 +0200
> > Pavel Machek <pavel@....cz> wrote:
> > 
> > > On Wed 2011-09-28 07:52:40, Jeff Layton wrote:
> > > > Allow the wait_on_bit_killable sleeps in SUNRPC layer to respect
> the
> > > > freezer. This should allow suspend and hibernate events to occur,
> > > > even when there are RPC's pending on the wire.
> > >
> > > Will the RPC protocols used handle that correctly? What will happen
> > > during resume?
> > >
> > 
> > That depends on the state of the socket during resume. If the
> > suspend/resume is quick enough, then the socket may still be
> connected, or
> > if we're using UDP then we might just get the reply and carry on
> successfully.
> > Otherwise, the call will eventually time out, or will be cancelled
> when the
> > kernel finds that the socket has been closed.
> > 
> > Either way, this should do the right thing.
> 
> Well... The problem when this sort of thing happens is with the replay
> cache. If the RPC in question was a mkdir, for instance, then replaying
> the RPC call when you wake up can be problematic because chances are
> that the server will have forgotten who created the directory, and so
> will reply with EEXIST instead of OK.
> However this is a generic problem when the client is unable to talk to
> the server for a while, and is not particular to suspend.
> 

Yeah, that's always a problem. You can hit the same thing if you just
unplug the cable from the network interface at an inopportune time.

I think this patch is really the best we can do under those
circumstances. Eventually we'll all be on 4.1 with sessions and this
problem will go away, right? ;)

-- 
Jeff Layton <jlayton@...hat.com>
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