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 16:04:55 +0800
Message-ID: <50C6E927.9040605@cn.fujitsu.com>
References: <50C18168.305@cn.fujitsu.com> <20121210203014.GB2402@amt.cnet>
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Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Gleb Natapov <gleb@redhat.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: Marcelo Tosatti <mtosatti@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <20121210203014.GB2402@amt.cnet>
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 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 compari=
son 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/kex=
ec.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;
>=20
> Isnt this (__rcu AS tag) sufficient? After all, sparse is complaining
> about namespaces.
>=20
> Creating a #define to cast seems excessive.
>=20
>=20

I am not very familiar with the rcu.
Adding __rcu tag could solve the problem. But it imported another warni=
ng
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 (d=
ifferent modifiers)
arch/x86/kernel/crash.c:49:30:    expected void ( *do_vmclear_operation=
 )( ... )
arch/x86/kernel/crash.c:49:30:    got void ( [noderef] *<noident> )( ..=
=2E )
arch/x86/kernel/crash.c:49:30: warning: incorrect type in assignment (d=
ifferent modifiers)
arch/x86/kernel/crash.c:49:30:    expected void ( *do_vmclear_operation=
 )( ... )
arch/x86/kernel/crash.c:49:30:    got void ( [noderef] *<noident> )( ..=
=2E )

So I made the #define to cast its type.

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

Thanks
Zhang Yanfei