linux-kernel - Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make fake_signal_wake_up() wake TASK

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Date:	Tue, 1 Nov 2011 19:13:29 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Jeff Layton <jlayton@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Steve French <sfrench@...ba.org>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-cifs@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Neil Brown <neilb@...e.de>, trond.myklebust@...app.com,
	linux-nfs@...r.kernel.org
Subject: Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make
	fake_signal_wake_up() wake TASK_KILLABLE tasks too"

On 11/01, Tejun Heo wrote:
>
> Yeah yeah, Trond already pointed it out.  I forgot about the
> sigpending special case in schedule(), which I think is rather odd,

I disagree with "rather odd" ;)

We have a lot of examples of

	current->state = TASK_INTERRUPTIBLE;
	...
	if (signal_pending())
		break;
	schedule();

Without that special case in schedule() the code above becomes racy.
Just consider __wait_event_interruptible().

> Any better ideas?

Well. As a simple (probably temporary) fix, I'd suggest

	#define wait_event_freezekillable(wq, condition)
	{
		freezer_do_not_count();
		__retval = wait_event_killable(condition);
		freezer_count();
		__retval;
	}

Do you think it can work?

Oleg.

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