Re: [PATCH 7/7] preempt: Take away preempt_enable_no_resched() frommodules

[Jacob Pan]

On Wed, 20 Nov 2013 17:04:57 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
> Cc: lenb@xxxxxxxxxx
> Cc: rjw@xxxxxxxxxxxxx
> Cc: Eliezer Tamir <eliezer.tamir@xxxxxxxxxxxxxxx>
> Cc: Chris Leech <christopher.leech@xxxxxxxxx>
> Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> Cc: rui.zhang@xxxxxxxxx
> Cc: jacob.jun.pan@xxxxxxxxxxxxxxx
> Cc: Mike Galbraith <bitbucket@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: hpa@xxxxxxxxx
> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
>  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 ârcu_read_unlock_sched_notraceâ:
include/linux/rcupdate.h:889:2: error: implicit declaration of function
âpreempt_enable_no_resched_notraceâ [-Werror=implicit-function-declaration]

2)
In file included from drivers/cpufreq/acpi-cpufreq.c:41:0:
include/linux/uaccess.h: In function âpagefault_enableâ:
include/linux/uaccess.h:34:2: error: implicit declaration of function
âpreempt_check_reschedâ [-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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