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

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Message-ID: <20130306181608.GA18687@redhat.com>
Date:	Wed, 6 Mar 2013 19:16:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	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 03/05, Tejun Heo wrote:
>
> Oleg, are you still opposed to the idea of making freezer share trap
> points with ptrace?

My memory can fool me, but iirc I wasn't actually opposed... I guess
you mean the previous discussion about vfork/ptrace/etc which I forgot
completely.

But I can recall the main problem with your idea (with me): I simply
wasn't able to understand it ;)

Likewise, I can't really understand the ideas discussed in this thread.
At least when it come to this particular problem, rpc_wait_bit_killable()
is not interruptible...

And how SIGFREEZE can help? If we want to interrupt the sleeps in NFS/RPC
layer we can simply add TASK_WAKEFREEZE (can be used with TASK_KILLABLE)
and change freeze_task() to do signal_wake_up_state(TASK_WAKEFREEZE).

But if we can do this, then it should be possible so simply make these
sleeps TASK_INTERRUPTIBLE ? But it seems that we can't just because we
can't always restart, so I am totally confused.

Oleg.

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