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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Date:	Thu, 14 Feb 2013 11:41:16 +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 Wed, Feb 13, 2013 at 10:21 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, February 13, 2013 06:34:16 PM Miklos Szeredi wrote:

>>
>> So I think the PF_FREEZE_DAEMON idea (the patch from Li Fei that
>> started this thread) may still be our best bet at handling this
>> situation.  The idea being that pure "originator" processes (ones that
>> take no part in serving filesystem syscalls) can be frozen up-front.
>> Then the "fuse daemon" (or "server") processes are hopefully in a
>> quiescent state and can be frozen without difficulty.
>>
>> Unfortunately it needs help from userspace: the kernel can't easily
>> guess which processes are part of a "fuse daemon" and which aren't.
>> Fortunately we have a standard library (libfuse) that can tell it to
>> the kernel for the vast majority of cases.
>
> So basically the idea would be to introduce something like PF_FREEZE_LATE
> for user space processes that need to be frozen after all of the other
> (non-PF_FREEZE_LATE) user space processes have been frozen and hack fuse
> to use that flag?

Yes.

It is essentially the same mechanism that is used to delay the
freezing of kernel threads after userspace tasks have been frozen.
Except it's a lot more difficult to determine which userspace tasks
need to be suspended late and which aren't.

Thanks,
Miklos
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