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

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Message-ID: <CAMbhsRTSCW3WOxTgw8btk2yWAucqNmyY-Sc+CHsHmZzf6ZsTNA@mail.gmail.com>
Date:	Thu, 2 May 2013 19:41:39 -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 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?
>
> On Thu, May 2, 2013 at 5:03 PM, Tejun Heo <tj@...nel.org> wrote:
>> On Thu, May 02, 2013 at 04:55:05PM -0700, Tejun Heo wrote:
>>> So, the freezable interface can't be something that people can use
>>> casually.  It is something which should be carefully and strategically
>>> deployed where we *know* that lock dependency risks don't exist or at
>>> least are acceptable.  I'm a bit weary that this patch is expanding
>>> the interface a lot that they now look like the equivalents of normal
>>> schedule calls.  Not exactly sure what to do here but can we please at
>>> least have RED BOLD BLINKING comments which scream to people not to
>>> use these unless they know what they're doing?
>>
>> Maybe we should trigger WARN_ON_ONCE() if lockdep_depth() > 0 by
>> default and have ugly variants which can be used if the caller is sure
>> that it's okay possibly with list of locks which are held?
>>
>> --
>> tejun

(sorry for the top post)

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.
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