linux-kernel - Re: [PATCH] module: Prevent recursion bug caused by module RCU check

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Message-ID: <8737x4g6c7.fsf@rustcorp.com.au>
Date:	Wed, 21 Oct 2015 15:34:40 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] module: Prevent recursion bug caused by module RCU check

Peter Zijlstra <peterz@...radead.org> writes:
> On Tue, Oct 20, 2015 at 06:53:31PM +0200, Peter Zijlstra wrote:
>> Also, would it not be better to fix WARN_ON_ONCE() instead?
>> 
>
> Clearly I'm an idiot and should stay away from the computer...

Acked-by: Rusty Russell <rusty@...tcorp.com.au>

(I mean, the patch, not the comment on Peter's intellect!  If he's too
 dumb to go near computers, most of us should probably shy away from
 anything with buttons....)

Thanks,
Rusty.

> ---
>  include/asm-generic/bug.h | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index 630dd2372238..d0972fc8433f 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -110,9 +110,10 @@ extern void warn_slowpath_null(const char *file, const int line);
>  	static bool __section(.data.unlikely) __warned;		\
>  	int __ret_warn_once = !!(condition);			\
>  								\
> -	if (unlikely(__ret_warn_once))				\
> -		if (WARN_ON(!__warned)) 			\
> -			__warned = true;			\
> +	if (unlikely(__ret_warn_once && !__warned)) {		\
> +		__warned = true;				\
> +		WARN_ON(1);					\
> +	}							\
>  	unlikely(__ret_warn_once);				\
>  })
>  
> @@ -120,9 +121,10 @@ extern void warn_slowpath_null(const char *file, const int line);
>  	static bool __section(.data.unlikely) __warned;		\
>  	int __ret_warn_once = !!(condition);			\
>  								\
> -	if (unlikely(__ret_warn_once))				\
> -		if (WARN(!__warned, format)) 			\
> -			__warned = true;			\
> +	if (unlikely(__ret_warn_once && !__warned)) {		\
> +		__warned = true;				\
> +		WARN(1, format);				\
> +	}							\
>  	unlikely(__ret_warn_once);				\
>  })
>  
--
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