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

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Date:	Wed, 6 Mar 2013 13:31:10 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, Jeff Layton <jlayton@...hat.com>,
	"Myklebust, Trond" <Trond.Myklebust@...app.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 Wed, Mar 6, 2013 at 1:24 PM, Tejun Heo <tj@...nel.org> wrote:
>
> With syscall paths out of the way, the surface is reduced a lot.

So the issue is syscalls that don't react to signals, and that can
potentially wait a long time.

Like NFS with a network hickup. Which is not at all unlikely. Think
wireless network, somebody trying to get on a network share, things
not working, and closing the damn lid because you give up.

So I do agree that we probably have *too* many of the stupid "let's
check if we can freeze", and I suspect that the NFS code should get
rid of the "freezable_schedule()" that is causing this warning
(because I also agree that you should *not* freeze while holding
locks, because it really can cause deadlocks), but I do suspect that
network filesystems do need to have a few places where they check for
freezing on their own... Exactly because freezing isn't *quite* like a
signal.

                 Linus
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