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 11:06:01 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Tue, Nov 01, 2011 at 06:59:53PM +0100, Oleg Nesterov wrote:
> > #define wait_event_freezekillable(wq, condition)			\
> > do {									\
> > 	DEFINE_WAIT(__wait);						\
> > 	for (;;) {							\
> > 		prepare_to_wait(&wq, &__wait, TASK_INTERRUPTIBLE);	\
> > 		if (condition || fatal_signal_pending(current))		\
> > 			break;						\
> > 		schedule();						\
> 
> No, this can't work, afaics.
> 
> Once the caller recieves a non-fatal signal (gets TIF_SIGPENDING),
> schedule() won't block in TASK_INTERRUPTIBLE state.
> 
> IOW, wait_event_freezekillable() becomes a busy-wait loop.

Yeah yeah, Trond already pointed it out.  I forgot about the
sigpending special case in schedule(), which I think is rather odd, oh
well.  Any better ideas?

-- 
tejun
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