linux-kernel - Re: [PATCH v2 03/10] freezer: add new freezable helpers using freezer_do_not

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Date:	Thu, 2 May 2013 21:17:21 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Jeff Layton <jlayton@...hat.com>,
	Mandeep Baines <msb@...omium.org>
Subject: Re: [PATCH v2 03/10] freezer: add new freezable helpers using freezer_do_not_count()

On Thu, May 2, 2013 at 9:09 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Thu, May 02, 2013 at 07:41:39PM -0700, Colin Cross wrote:
>> On Thu, May 2, 2013 at 7:16 PM, Colin Cross <ccross@...roid.com> wrote:
>> > This sounds the same as what ended up getting reverted in
>> > https://lkml.org/lkml/2013/3/4/221
>> > I can add the WARN_ON_ONCE to all my new calls, and leave them out of
>> > existing calls, but that seems a little odd, and will be redundant if
>> > the lockdep call in try_to_freeze goes back in in 3.11.  Do you still
>> > want it in the new apis?
> ...
>> I could also put the lockdep check that was reveted back into
>> try_to_freeze(), and add a freezable_schedule_unsafe() that skips it
>> for use in the known-unsafe users in nfs, with a big comment not to
>> add new users of it.
>
> Oh yeah, that sounds like a good idea, and as for the non-ugly
> variants, at least in the mid/long term, I think it'd be best to add
> the lockdep annotation to try_to_freeze() with
> __try_to_freeze_unsafe_youre_gonna_burn_in_hell_if_you_use_this() for
> the existing users which should be gradually converted, but if that's
> too burdensome, adding warnings to the wrappers should do for now, I
> guess.
>
> And I *hope* the lockdep annotation is stricter than what was added
> before.  I think it better be "no lock ever should be held at this
> point" rather than "consider this a big lock".

The previous patch (6aa9707099c4b25700940eb3d016f16c4434360d in Linus'
tree) already required that no locks be held, it wasn't using a lock
annotation.
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