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

From: Miklos Szeredi
Date: Mon Feb 11 2013 - 05:11:48 EST

On Mon, Feb 11, 2013 at 12:31 AM, Rafael J. Wysocki <rjw@xxxxxxx> 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...

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