linux-kernel - Re: [PATCH RFC] vfs: make fstatat retry on ESTALE errors from getattr call

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Date:	Mon, 16 Apr 2012 20:25:06 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Jeff Layton <jlayton@...hat.com>
CC:	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>,
	Malahal Naineni <malahal@...ibm.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pstaubach@...grid.com" <pstaubach@...grid.com>,
	"miklos@...redi.hu" <miklos@...redi.hu>,
	"viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
	"hch@...radead.org" <hch@...radead.org>,
	"michael.brantley@...haw.com" <michael.brantley@...haw.com>,
	"sven.breuner@...m.fraunhofer.de" <sven.breuner@...m.fraunhofer.de>
Subject: Re: [PATCH RFC] vfs: make fstatat retry on ESTALE errors from
 getattr call

On Mon, 2012-04-16 at 15:43 -0400, Jeff Layton wrote:
> On Mon, 16 Apr 2012 19:33:05 +0000
> "Myklebust, Trond" <Trond.Myklebust@...app.com> wrote:
> 
> > On Mon, 2012-04-16 at 13:46 -0400, Jeff Layton wrote:
> > > The question about looping indefinitely really comes down to:
> > > 
> > > 1) is a persistent ESTALE in conjunction with a successful lookup a
> > > situation that we expect to be temporary. i.e. will the admin at some
> > > point be able to do something about it? If not, then there's no point
> > > in continuing to retry. Again, this is a situation that *really* should
> > > not happen if the filesystem is doing the right thing.
> > > 
> > > 2) If the admin can't do anything about it, is it reasonable to expect
> > > that users can send a fatal signal to hung applications if this
> > > situation occurs.
> > > 
> > > We expect that that's ok in other situations to resolve hung
> > > applications, so I'm not sure I understand why it wouldn't be
> > > acceptable here...
> > 
> > There are definitely potentially persistent pathological situations that
> > the filesystem can't do anything about. If the point of origin for your
> > pathname (for instance your current directory in the case of a relative
> > pathname) is stale, then no amount of looping is going to help you to
> > recover.
> > 
> 
> Ok -- Peter pretty much said something similar. Retrying indefnitely
> when the lookup returns ESTALE probably won't help. I'm ok with
> basically letting the VFS continue to do what it does there already. If
> it gets an ESTALE, it tries again with LOOKUP_REVAL set and then gives
> up if that doesn't work.
> 
> If however, the operation itself keeps returning ESTALE, are we OK to
> retry indefinitely assuming that we'll break out of the loop on fatal
> signals?
>
> For example, something like the v2 patch I sent a little while ago?


Won't something like fstatat(AT_FDCWD, "", &stat, AT_EMPTY_PATH) risk
looping forever there, or am I missing something?

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com