From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pan Xinhui Subject: Re: [PATCH] acpi-cpufreq: Add a miss ifdef CONFIG_X86_ACPI_CPUFREQ_CPB Date: Tue, 14 Jul 2015 10:09:47 +0800 Message-ID: <55A46F6B.6030006@intel.com> References: <559F5D13.8050104@intel.com> <55A35BA4.8020800@intel.com> <1591472.jfYRX9HXXv@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mga09.intel.com ([134.134.136.24]:10930 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751885AbbGNCM1 (ORCPT ); Mon, 13 Jul 2015 22:12:27 -0400 In-Reply-To: <1591472.jfYRX9HXXv@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: "Rafael J. Wysocki" , Linux Kernel Mailing List , "linux-pm@vger.kernel.org" , Viresh Kumar , "yanmin_zhang@linux.intel.com" , "mnipxh@163.com" hi, Rafael, thanks for you reply :) On 2015=E5=B9=B407=E6=9C=8814=E6=97=A5 07:26, Rafael J. Wysocki wrote: > On Monday, July 13, 2015 02:33:08 PM Pan Xinhui wrote: >> hi, Rafeal >> thanks for your reply. :) >> >> On 2015=E5=B9=B407=E6=9C=8811=E6=97=A5 04:44, Rafael J. Wysocki wrot= e: >>> Hi, >>> >>> On Fri, Jul 10, 2015 at 7:50 AM, Pan Xinhui = wrote: >>>> >>>> If CONFIG_X86_ACPI_CPUFREQ_CPB has not been defined, the placehold= er for >>>> cpb is not needed. Add ifdef around it. >>>> >>>> Signed-off-by: Pan Xinhui >>>> --- >>>> drivers/cpufreq/acpi-cpufreq.c | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi= -cpufreq.c >>>> index e7fcaa6..314a19e 100644 >>>> --- a/drivers/cpufreq/acpi-cpufreq.c >>>> +++ b/drivers/cpufreq/acpi-cpufreq.c >>>> @@ -884,7 +884,9 @@ static int acpi_cpufreq_resume(struct cpufreq_= policy *policy) >>>> static struct freq_attr *acpi_cpufreq_attr[] =3D { >>>> &cpufreq_freq_attr_scaling_available_freqs, >>>> &freqdomain_cpus, >>>> +#ifdef CONFIG_X86_ACPI_CPUFREQ_CPB >>>> NULL, /* this is a placeholder for cpb, do not remove */ >>>> +#endif >>> >>> Adding the ifdef here doesn't change anything, because the next NUL= L >>> will play the role of the one you've just #ifdefed and the structur= e >>> will be filled with zeros from that point on anyway. >>> >> Yes, adding ifdef here does not change any binary codes. But I want = to make the codes more readable. :) >> Patch author has noticed two *NULL* here would confuse people, espec= ially who first read this acpi-cpufreq.c file >> From code style point, it would be better to have #ifdef around it.=20 >=20 > Not really. >=20 > Why don't you simply drop *both* NULLs? >=20 Just like string end with *NULL* :) 1021 static int cpufreq_add_dev_interface(struct cpufreq_policy *policy= , 1022 struct device *dev) 1023 { 1024 struct freq_attr **drv_attr; 1025 int ret =3D 0; 1026=20 1027 /* set up files for this cpu device */ 1028 drv_attr =3D cpufreq_driver->attr; 1029 while (drv_attr && *drv_attr) { 1030 ret =3D sysfs_create_file(&policy->kobj, &((*drv_attr)->at= tr)); 1031 if (ret) 1032 return ret; 1033 drv_attr++; 1034 } If struct freq_attr *acpi_cpufreq_attr[] did not end with NULL, line 10= 33 will access invalid data area. If *drv_attr(the data after struct freq_attr * array[]) happened to be = not NULL. panic may hit in sysfs_create_file :( So at least one *NULL* must be in the end of freq_attr *array[]. Actually in acpi-cpufreq.c, in acpi_cpufreq_init function. 957 struct freq_attr **iter; 958=20 959 pr_debug("adding sysfs entry for cpb\n"); 960=20 961 for (iter =3D acpi_cpufreq_attr; *iter !=3D NULL; iter++) 962 ; 963=20 964 /* make sure there is a terminator behind it */ 965 if (iter[1] =3D=3D NULL) 966 *iter =3D &cpb; 967 } line965, check of iter[1] is not needed. Maybe the patch author was afr= aid of an unexpected remove of first *NULL*. It might be a better solution to add ifdef CONFIG_X86_ACPI_CPUFREQ_CPB = around that *NULL*, and remove this !iter[1] check. thanks xinhui >=20 >> >>> You'd need to #ifdef it in the struct freq_attr definition, but I'm >>> not sure it's worth the effort. >>> >> >> struct freq_attr *cpb* is defined in #ifdef section. :) >=20 > Ah, OK. >=20 >=20