linux-kernel - Re: Getting rid of freezer for suspend [was Re: [fuse-devel] [PATCH] fuse: make fuse daemon frozen along with kernel threads]

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Message-ID: <CAJfpegtNUr+AJXZcKmLEGBYqu20DVFwzg-OvOk_nS3fBS3wd=Q@mail.gmail.com>
Date:	Mon, 11 Feb 2013 11:11:40 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>,
	Goswin von Brederlow <goswin-v-b@....de>,
	Li Fei <fei.li@...el.com>, len.brown@...el.com,
	mingo@...hat.com, peterz@...radead.org, biao.wang@...el.com,
	linux-pm@...r.kernel.org, fuse-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, chuansheng.liu@...el.com
Subject: Re: Getting rid of freezer for suspend [was Re: [fuse-devel] [PATCH]
 fuse: make fuse daemon frozen along with kernel threads]

On Mon, Feb 11, 2013 at 12:31 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Sunday, February 10, 2013 07:55:05 PM Pavel Machek wrote:

>> Well, from freezer you need:
>>
>> 1) user process frozen.
>>
>> 2) essential locks _not_ held so that block devices are still functional.
>>
>> > > > mmap... what is problem with mmap? For suspend, memory is powered, so
>> > > > you can permit people changing it.
>> > >
>> > > Suppose mmap is used to make the registers of some device available to user
>> > > space.  Yes, that can happen.
>>
>> "Don't do it, then". Yes, can happen, but hopefully is not too common
>> these days. [And... freezer doing 1) but not 2) would be enough to
>> handle that. Freezer doing 1) but not 2) would also be simpler...]
>
> Again, I'm not sure what you mean.
>
> Are you trying to say that it would be OK to freeze user space tasks in
> the D state?

I think that's what Pavel is saying.   Processes in D state sleeping
on non-device mutexes _are_ actually OK to freeze.  And that would
nicely solve the fuse freeze problem.  The only little detail is how
do we implement that...

Thanks,
Miklos
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