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

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Message-ID: <CA+55aFySyBP8q5AvPrt-s_ZPdgamfoX-dERw4EJ21EcsDLBjYA@mail.gmail.com>
Date:	Thu, 7 Mar 2013 08:25:10 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Myklebust, Trond" <Trond.Myklebust@...app.com>
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, Mar 7, 2013 at 7:59 AM, Myklebust, Trond
<Trond.Myklebust@...app.com> wrote:
>
> It _shouldn't_ be an interruption unless the filesystem can't make
> progress.

So how can we tell? Calling "freezable_schedule()" if you're not ready
to be frozen is not good. And nobody but the NFS code can know.

You might want to introduce some counter that counts number of
outstanding non-interruptible events, and only call the "freezable"
version if that counter is zero.

A better alternative might be to *never* call the freezable version.
Because those freezable_*() things are really quite disgusting, and
are wrong - they don't actually freeze the process, they say "I don't
care if you freeze me while I sleep", and you might actually wake up
*while* the system is being frozen. I think the whole concept is
broken. Rafaei - comments? The function really is crap, regardless of
any unrelated NFS problems.

So what NFS could do instead is actually check the "do I need to
freeze" flag, and if you need to freeze you consider it an abort - and
do *not* try to continue. Just freeze, and then act as if the machine
got rebooted as far as NFS was concerned. That should work anyway, no?

That does sound a lot more complex, though.

                 Linus
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