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 18:59:53 +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:
>
> diddling with
> sigmask in kernel generally isn't a good idea.

Agreed.

> If there are only a handful sites which need this type of behavior,
> wouldn't something like the following work?
>
> #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.

Oleg.

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