linux-kernel - Re: [PATCH] kernel: context_tracking: use extern function instead of static inline function for user

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Date:	Wed, 23 Oct 2013 06:47:24 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>, khilman@...aro.org,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kernel: context_tracking: use extern function instead
 of static inline function for user_enter/exit()

On Wed, 2013-10-23 at 18:38 +0800, Chen Gang wrote:

> 
> Signed-off-by: Chen Gang <gang.chen@...anux.com>
> ---
>  include/linux/context_tracking.h |   14 ++------------
>  kernel/context_tracking.c        |   12 ++++++++++++
>  2 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index 1581587..bf220f7 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -10,23 +10,13 @@
>  #ifdef CONFIG_CONTEXT_TRACKING
>  extern void context_tracking_cpu_set(int cpu);
>  
> +extern void user_enter(void);
> +extern void user_exit(void);
>  extern void context_tracking_user_enter(void);
>  extern void context_tracking_user_exit(void);
>  extern void __context_tracking_task_switch(struct task_struct *prev,
>  					   struct task_struct *next);
>  
> -static inline void user_enter(void)
> -{
> -	if (static_key_false(&context_tracking_enabled))
> -		context_tracking_user_enter();
> -
> -}
> -static inline void user_exit(void)
> -{
> -	if (static_key_false(&context_tracking_enabled))
> -		context_tracking_user_exit();
> -}
> -
>  static inline enum ctx_state exception_enter(void)
>  {
>  	enum ctx_state prev_ctx;
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 013161f..c03d0d6 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -29,6 +29,18 @@ EXPORT_SYMBOL_GPL(context_tracking_enabled);
>  DEFINE_PER_CPU(struct context_tracking, context_tracking);
>  EXPORT_SYMBOL_GPL(context_tracking);
>  
> +void user_enter(void)
> +{
> +	if (static_key_false(&context_tracking_enabled))
> +		context_tracking_user_enter();
> +}
> +
> +void user_exit(void)
> +{
> +	if (static_key_false(&context_tracking_enabled))
> +		context_tracking_user_exit();
> +}
> +
>  void context_tracking_cpu_set(int cpu)
>  {
>  	if (!per_cpu(context_tracking.active, cpu)) {

Ug, you just put an unneeded function call into a fast path because of a
failure with a particular arch.

If you need the assembly to call this code, then make yourself a wrapper
function to call that does the user_enter/exit() calls.

void arch_user_enter(void)
{
	user_enter();
}

-- Steve


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