linux-kernel - Re: LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held!

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Message-ID: <4FA345DA4F4AE44899BD2B03EEEC2FA9286B5452@sacexcmbx05-prd.hq.netapp.com>
Date:	Thu, 7 Mar 2013 17:16:12 +0000
From:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Jeff Layton <jlayton@...hat.com>, Tejun Heo <tj@...nel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Mandeep Singh Baines <msb@...omium.org>,
	Ming Lei <ming.lei@...onical.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held!

On Thu, 2013-03-07 at 09:03 -0800, Linus Torvalds wrote:
> On Thu, Mar 7, 2013 at 8:45 AM, Myklebust, Trond
> <Trond.Myklebust@...app.com> wrote:
> >
> > The problem there is that we get into the whole 'hard' vs 'soft' mount
> > problem. We're supposed to guarantee data integrity for 'hard' mounts,
> > so no funny business is allowed. OTOH, 'soft' mounts time out and return
> > EIO to the application anyway, and so shouldn't be a problem.
> >
> > Perhaps we could add a '-oslushy' mount option :-) that guarantees data
> > integrity for all situations _except_ ENETDOWN/ENETUNREACH?
> 
> I do think we are probably over-analyzing this. It's not like people
> who want freezing to work usually use flaky NFS. There's really two
> main groups:
> 
>  - the "freezer as a snapshot mechanism" that might use NFS because
> they are in a server environment.
> 
>  - the "freeezer for suspend/resume on a laptop"
> 
> The first one does use NFS, and cares about it, and probably would
> prefer the freeze event to take longer and finish for all ongoing IO
> operations. End result: just ditch the "freezable_schedule()"
> entirely.
> 
> The second one is unlikely to really use NFS anyway. End result:
> ditching the freezable_schedule() is probably perfectly fine, even if
> it would cause suspend failures if the network is being troublesome.
> 
> So for now, why not just replace freezable_schedule() with plain
> schedule() in the NFS code, and ignore it until somebody actually
> complains about it, and then aim to try to do something more targeted
> for that particular complaint?

We _have_ had complaints about the laptop suspension problem; that was
why Jeff introduced freezable_schedule() in the first place. We've never
had complaints about any problems involvinf cgroup_freeze. This is why
our focus tends to be on the former, and why I'm more worried about
laptop suspend regressions for any short term fixes.

-- 
Trond Myklebust
Linux NFS client maintainer

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