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Date: Tue, 1 Nov 2011 19:13:29 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: Jeff Layton <jlayton@redhat.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
        Steve French <sfrench@samba.org>, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org, linux-cifs@vger.kernel.org,
        "J. Bruce Fields" <bfields@fieldses.org>, Neil Brown <neilb@suse.de>,
        trond.myklebust@netapp.com, linux-nfs@vger.kernel.org
Subject: Re: [RFC PATCH] freezer: revert 27920651fe "PM / Freezer: Make
	fake_signal_wake_up() wake TASK_KILLABLE tasks too"
Message-ID: <20111101181329.GA6739@redhat.com>
References: <20111031221743.GA18855@google.com> <201111010024.16659.rjw@sisk.pl> <20111031233059.GI18855@google.com> <20111101005505.GO18855@google.com> <20111101041337.39077229@tlielax.poochiereds.net> <20111101065958.50addab5@tlielax.poochiereds.net> <20111101163059.GR18855@google.com> <20111101175953.GB5358@redhat.com> <20111101180601.GV18855@google.com>
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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.