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

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Message-ID: <20151020142026.60e64a9e@gandalf.local.home>
Date:	Tue, 20 Oct 2015 14:20:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] module: Prevent recursion bug caused by module RCU
 check

On Tue, 20 Oct 2015 19:09:05 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> 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...

Hehe,

> 
> ---
>  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);				\
>  })

I thought about it too, but was too busy to think harder about it. I
may have made the same mistakes as you.

-- Steve

>  
> @@ -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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