linux-kernel - Re: [RFC][PATCH 1/2] Freezer: Introduce PF_FREEZER

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Message-ID: <20080507093621.GF13858@elf.ucw.cz>
Date:	Wed, 7 May 2008 11:36:21 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	pm list <linux-pm@...ts.linux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Cedric Le Goater <clg@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [RFC][PATCH 1/2] Freezer: Introduce PF_FREEZER_NOSIG

Hi!

> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> The freezer currently attempts to distinguish kernel threads from
> user space tasks by checking if their mm pointer is unset and it
> does not send fake signals to kernel threads.  However, there are
> kernel threads, mostly related to networking, that behave like
> user space tasks and may want to be sent a fake signal to be frozen.
> 
> Introduce the new process flag PF_FREEZER_NOSIG that will be set
> by default for all kernel threads and make the freezer only send
> fake signals to the tasks having PF_FREEZER_NOSIG unset.  Provide
> the set_freezable_with_signal() function to be called by the kernel
> threads that want to be sent a fake signal for freezing.
> 
> This patch should not change the freezer's observable behavior.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>

ACK.


> -static int has_mm(struct task_struct *p)
> +static inline bool should_send_signal(struct task_struct *p)
>  {
> -	return (p->mm && !(p->flags & PF_BORROWED_MM));
> +	return !(current->flags & PF_FREEZER_NOSIG);
>  }
>

Note that we used to tell kernel threads by ->mm, and now you assume
that anything created by ktrheadd is kernel thread, ->mm or not.

I'm not sure if those can differ (->mm = NULL somewhere? Or ->mm =
something somewhere else?). I guess this should go to -mm for a long
test...

> @@ -234,7 +234,7 @@ int kthreadd(void *unused)
>  	set_user_nice(tsk, KTHREAD_NICE_LEVEL);
>  	set_cpus_allowed(tsk, CPU_MASK_ALL);
>  
> -	current->flags |= PF_NOFREEZE;
> +	current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
>  
>  	for (;;) {
>  		set_current_state(TASK_INTERRUPTIBLE);

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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