linux-kernel - Re: [PATCH 1/2] PM / Freezer: Remove the "userspace only" constraint from freezer[_do_not]

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Message-Id: <201112062336.40846.rjw@sisk.pl>
Date:	Tue, 6 Dec 2011 23:36:40 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, pavel@....cz, len.brown@...el.com,
	tj@...nel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] PM / Freezer: Remove the "userspace only" 
 	constraint from freezer[_do_not]_count()

On Tuesday, December 06, 2011, Srivatsa S. Bhat wrote:
> On 12/06/2011 10:50 PM, Oleg Nesterov wrote:
> 
> > On 12/06, Srivatsa S. Bhat wrote:
> >>
> >> And moreover, even the vfork issue does not need
> >> the above restriction in these functions, since they are anyway called by
> >> userspace processes.
> > 
> > This looks a bit confusing, as if CLONE_VFORK is not used by kthreads.
> > It is actually used, but only by the non-freezeable workqueue threads,
> > so the patch is fine.
> > 
> > Reviewed-by: Oleg Nesterov <oleg@...hat.com>
> > 
> 
> 
> Thank you! I have updated the commit message by omitting the confusing part:
> 
> ---
> From: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> [PATCH 1/2] PM / Freezer: Remove the "userspace only" constraint from freezer[_do_not]_count()
> 
> At present, the functions freezer_count() and freezer_do_not_count()
> impose the restriction that they are effective only for userspace processes.
> However, now, these functions have found more utility than originally
> intended by the commit which introduced it: ba96a0c8 (freezer:
> fix vfork problem). And moreover, even the vfork issue actually does not
> need the above restriction in these functions.
> 
> So, modify these functions to make them work even for kernel threads, so
> that they can be used at other places in the kernel, where the userspace
> restriction doesn't apply.
> 
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Suggested-by: Tejun Heo <tj@...nel.org>
> Acked-by: Tejun Heo <tj@...nel.org>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Applied to linux-pm/linux-next ([2/2] too).

Thanks,
Rafael


> ---
> 
>  include/linux/freezer.h |   28 +++++++++++-----------------
>  1 files changed, 11 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/freezer.h b/include/linux/freezer.h
> index 30f06c2..7bcfe73 100644
> --- a/include/linux/freezer.h
> +++ b/include/linux/freezer.h
> @@ -67,33 +67,27 @@ static inline bool cgroup_freezing(struct task_struct *task)
>   * appropriately in case the child has exited before the freezing of tasks is
>   * complete.  However, we don't want kernel threads to be frozen in unexpected
>   * places, so we allow them to block freeze_processes() instead or to set
> - * PF_NOFREEZE if needed and PF_FREEZER_SKIP is only set for userland vfork
> - * parents.  Fortunately, in the ____call_usermodehelper() case the parent won't
> - * really block freeze_processes(), since ____call_usermodehelper() (the child)
> - * does a little before exec/exit and it can't be frozen before waking up the
> - * parent.
> + * PF_NOFREEZE if needed. Fortunately, in the ____call_usermodehelper() case the
> + * parent won't really block freeze_processes(), since ____call_usermodehelper()
> + * (the child) does a little before exec/exit and it can't be frozen before
> + * waking up the parent.
>   */
>  
> -/*
> - * If the current task is a user space one, tell the freezer not to count it as
> - * freezable.
> - */
> +
> +/* Tell the freezer not to count the current task as freezable. */
>  static inline void freezer_do_not_count(void)
>  {
> -	if (current->mm)
> -		current->flags |= PF_FREEZER_SKIP;
> +	current->flags |= PF_FREEZER_SKIP;
>  }
>  
>  /*
> - * If the current task is a user space one, tell the freezer to count it as
> - * freezable again and try to freeze it.
> + * Tell the freezer to count the current task as freezable again and try to
> + * freeze it.
>   */
>  static inline void freezer_count(void)
>  {
> -	if (current->mm) {
> -		current->flags &= ~PF_FREEZER_SKIP;
> -		try_to_freeze();
> -	}
> +	current->flags &= ~PF_FREEZER_SKIP;
> +	try_to_freeze();
>  }
>  
>  /*
> 
> 
> 
> 

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