linux-kernel - Re: [PATCH 7/7] preempt: Take away preempt_enable_no

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Date:	Wed, 20 Nov 2013 10:54:57 -0800
From:	Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Chris Leech <christopher.leech@...el.com>,
	David Miller <davem@...emloft.net>, rui.zhang@...el.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH 7/7] preempt: Take away preempt_enable_no_resched() from
 modules

On Wed, 20 Nov 2013 17:04:57 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> Discourage drivers/modules to be creative with preemption.
> 
> Sadly all is implemented in macros and inline so if they want to do
> evil they still can, but at least try and discourage some.
> 
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Cc: lenb@...nel.org
> Cc: rjw@...ysocki.net
> Cc: Eliezer Tamir <eliezer.tamir@...ux.intel.com>
> Cc: Chris Leech <christopher.leech@...el.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: rui.zhang@...el.com
> Cc: jacob.jun.pan@...ux.intel.com
> Cc: Mike Galbraith <bitbucket@...ine.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: hpa@...or.com
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
>  include/linux/preempt.h |   16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -64,7 +64,11 @@ do { \
>  } while (0)
>  
>  #else
> -#define preempt_enable() preempt_enable_no_resched()
> +#define preempt_enable() \
> +do { \
> +	barrier(); \
> +	preempt_count_dec(); \
> +} while (0)
>  #define preempt_check_resched() do { } while (0)
>  #endif
>  
> @@ -126,6 +130,16 @@ do { \
>  #define preempt_fold_need_resched() do { } while (0)
>  #endif
>  
> +#ifdef MODULE
> +/*
> + * Modules have no business playing preemption tricks.
> + */
> +#undef sched_preempt_enable_no_resched
> +#undef preempt_enable_no_resched
> +#undef preempt_enable_no_resched_notrace
> +#undef preempt_check_resched
> +#endif
> +
>  #ifdef CONFIG_PREEMPT_NOTIFIERS
>  
>  struct preempt_notifier;
> 
> 

run into a couple of compile issues.

1)
include/linux/rcupdate.h: In function ‘rcu_read_unlock_sched_notrace’:
include/linux/rcupdate.h:889:2: error: implicit declaration of function
‘preempt_enable_no_resched_notrace’ [-Werror=implicit-function-declaration]

2)
In file included from drivers/cpufreq/acpi-cpufreq.c:41:0:
include/linux/uaccess.h: In function ‘pagefault_enable’:
include/linux/uaccess.h:34:2: error: implicit declaration of function
‘preempt_check_resched’ [-Werror=implicit-function-declaration]

1) happens when CONFIG_PREEMPT is not set, perhaps add a dummy function?
2) I am not sure if we should take pagefault_enable away from modules
--
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