linux-kernel - Re: [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks"

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Date:	Thu, 16 Feb 2012 19:55:44 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Magnus Damm <magnus.damm@...il.com>, markgross@...gnar.org,
	Matthew Garrett <mjg@...hat.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	Brian Swetland <swetland@...gle.com>,
	Neil Brown <neilb@...e.de>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks"

2012/2/15 Rafael J. Wysocki <rjw@...k.pl>:
> On Wednesday, February 15, 2012, Arve Hjønnevåg wrote:
>> 2012/2/14 Rafael J. Wysocki <rjw@...k.pl>:
>> > On Tuesday, February 14, 2012, Arve Hjønnevåg wrote:
>> >> On Mon, Feb 6, 2012 at 5:00 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >> ...
>> >> but the wake-source timeout feature has some bugs or incompatible apis. An
>> >> init api would also be useful for embedding wake-sources in other data
>> >> structures without adding another memory allocation. Your patch to
>> >> move the spinlock init to wakeup_source_add still require the struct
>> >> to be zero initialized and the name set manually.
>> >
>> > That should be easy to fix.  What about the appended patch?
>> >
>>
>> That works, but I still have to call more than one function before I
>> can use the wakeup-source (wakeup_source_init and wakeup_source_add)
>> and more than one function before I can free it (__pm_relax,
>> wakeup_source_remove and wakeup_source_drop). Is there any reason to
>> keep these separate?
>
> Yes, there is.  I think that wakeup_source_create/_destroy() should
> use the same initialization functions internally that will be used for
> externally allocated wakeup sources (to make sure that all wakeup source
> objects are initialized in exactly the same way).
>

I agree with that, but is it useful to export these helper functions?

>> Also, not copying the name when the caller provides the memory for the
>> wakeup-source would be a closer match to the wakelock api. Most of our
>> wakelocks pass a string constant as the name, and making a copy of
>> that string is not useful. wake_lock_init is also safe to call from
>> atomic context, but I don't know if anyone relies on this.
>
> OK, below is another go.  It doesn't copy the name if wakeup_source_init() is
> used (which also does the _add this time).  I think, though, that copying
> the name is generally safer, because someone might use wakeup_source_init()
> with the name string allocated on the stack or otherwise temporary, which would
> be a bug with the new version.
>

I prefer this version. I have not seen a bug where someone passed a
temporary as the wakelock name, I assume since this will show up
immediately in the stats file.

-- 
Arve Hjønnevåg
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