From mboxrd@z Thu Jan  1 00:00:00 1970
From: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Subject: Re: [PATCH] x86/kexec: crash_vmclear_local_vmcss needs __rcu
Date: Tue, 11 Dec 2012 17:09:33 +0800
Message-ID: <50C6F84D.7010701@cn.fujitsu.com>
References: <50C18168.305@cn.fujitsu.com> <20121210203014.GB2402@amt.cnet> <50C6E927.9040605@cn.fujitsu.com> <20121211081024.GC11016@redhat.com>
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Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"kexec@lists.infradead.org" <kexec@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	kbuild test robot <fengguang.wu@intel.com>
To: Gleb Natapov <gleb@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20121211081024.GC11016@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

=E4=BA=8E 2012=E5=B9=B412=E6=9C=8811=E6=97=A5 16:10, Gleb Natapov =E5=86=
=99=E9=81=93:
> On Tue, Dec 11, 2012 at 04:04:55PM +0800, Zhang Yanfei wrote:
>> =E4=BA=8E 2012=E5=B9=B412=E6=9C=8811=E6=97=A5 04:30, Marcelo Tosatti=
 =E5=86=99=E9=81=93:
>>> 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 compa=
rison expression (different address spaces)
>>>>
>>>> Reported-by: kbuild test robot <fengguang.wu@intel.com>
>>>> Signed-off-by: Zhang Yanfei <zhangyanfei@cn.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/k=
exec.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
>>>> =20
>>>> -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))
>>>> =20
>>>>  #endif /* __ASSEMBLY__ */
>>>> =20
>>>> 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) =3D NULL;
>>>> +void __rcu (*crash_vmclear_loaded_vmcss)(void) =3D NULL;
>>>
>>> Isnt this (__rcu AS tag) sufficient? After all, sparse is complaini=
ng
>>> 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 wa=
rning
>> 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_operat=
ion )( ... )
>> 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_operat=
ion )( ... )
>> 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.
>>
> Try to use typedef.
>=20

Thanks. typedef works.