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

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Date:	Tue, 11 Dec 2012 16:04:55 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.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

于 2012年12月11日 04:30, Marcelo Tosatti 写道:
> 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.
> 
> 

I am not very familiar with the rcu.
Adding __rcu tag could solve the problem. But it imported another warning
when I try to assign rcu_dereference(crash_vmclear_loaded_vmcss) to
do_vmclear_operation:

arch/x86/kernel/crash.c:49:30: warning: incorrect type in assignment (different modifiers)
arch/x86/kernel/crash.c:49:30:    expected void ( *do_vmclear_operation )( ... )
arch/x86/kernel/crash.c:49:30:    got void ( [noderef] *<noident> )( ... )
arch/x86/kernel/crash.c:49:30: warning: incorrect type in assignment (different modifiers)
arch/x86/kernel/crash.c:49:30:    expected void ( *do_vmclear_operation )( ... )
arch/x86/kernel/crash.c:49:30:    got void ( [noderef] *<noident> )( ... )

So I made the #define to cast its type.

If you have any suggestion, that'll be helpful.

Thanks
Zhang Yanfei
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