Re: [RFC][PATCH 1/2] Freezer: Introduce PF_FREEZER_NOSIG

[Pavel Machek <pavel@suse.cz>]

Hi!

> From: Rafael J. Wysocki <rjw@sisk.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@sisk.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
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