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

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Message-ID: <1666707.98SRJWcGQW@vostro.rjw.lan>
Date:	Thu, 07 Mar 2013 21:55:13 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	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>,
	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 Thursday, March 07, 2013 08:25:10 AM Linus Torvalds wrote:
> 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?

Well, the only comment I have is that the source of these functions was
commit d310310c (Freezer / sunrpc / NFS: don't allow TASK_KILLABLE sleeps to
block the freezer) and they were added because people were complaining that
they couldn't suspend while their NFS servers were not responding, IIRC.

I agree that they are not really nice.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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