linux-kernel - Re: [PATCH] x86/kexec: crash_vmclear_local_vmcss needs _

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Date:	Mon, 10 Dec 2012 18:30:14 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Gleb Natapov <gleb@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kbuild test robot <fengguang.wu@...el.com>
Subject: Re: [PATCH] x86/kexec: crash_vmclear_local_vmcss needs __rcu

On Fri, Dec 07, 2012 at 01:40:56PM +0800, Zhang Yanfei wrote:
> This removes the sparse warning:
> arch/x86/kernel/crash.c:49:32: sparse: incompatible types in comparison expression (different address spaces)
> 
> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Signed-off-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>
> ---
>  arch/x86/include/asm/kexec.h |    4 +++-
>  arch/x86/kernel/crash.c      |    4 ++--
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
> index 28feeba..16882cd 100644
> --- a/arch/x86/include/asm/kexec.h
> +++ b/arch/x86/include/asm/kexec.h
> @@ -163,7 +163,9 @@ struct kimage_arch {
>  };
>  #endif
>  
> -extern void (*crash_vmclear_loaded_vmcss)(void);
> +extern void __rcu (*crash_vmclear_loaded_vmcss)(void);
> +#define vmclear_func_rcu(vmclear_func) \
> +	((void (*)(void)) rcu_dereference(vmclear_func))
>  
>  #endif /* __ASSEMBLY__ */
>  
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index 2f6b8e8..50ce1d6 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -38,7 +38,7 @@ int in_crash_kexec;
>   *
>   * protected by rcu.
>   */
> -void (*crash_vmclear_loaded_vmcss)(void) = NULL;
> +void __rcu (*crash_vmclear_loaded_vmcss)(void) = NULL;

Isnt this (__rcu AS tag) sufficient? After all, sparse is complaining
about namespaces.

Creating a #define to cast seems excessive.

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