linux-kernel - Re: [PATCH] test_firmware: remove unnecessary test_fw_mutex in test_dev_config_show

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Message-ID: <e2b95fde-0ab7-c0d1-2c64-cceffc458673@broadcom.com>
Date:   Wed, 15 Apr 2020 09:28:18 -0700
From:   Scott Branden <scott.branden@...adcom.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Luis Chamberlain <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Brown <david.brown@...aro.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Shuah Khan <shuah@...nel.org>, bjorn.andersson@...aro.org,
        Shuah Khan <skhan@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Olof Johansson <olof@...om.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Colin Ian King <colin.king@...onical.com>,
        Takashi Iwai <tiwai@...e.de>, linux-kselftest@...r.kernel.org,
        Andy Gross <agross@...nel.org>
Subject: Re: [PATCH] test_firmware: remove unnecessary test_fw_mutex in
 test_dev_config_show_xxx

Hi Kees,

On 2020-04-14 8:10 p.m., Kees Cook wrote:
> On Tue, Apr 14, 2020 at 05:25:17PM -0700, Scott Branden wrote:
>> Remove unnecessary use of test_fw_mutex in test_dev_config_show_xxx
>> functions that show simple bool, int, and u8.
> I would expect at least a READ_ONCE(), yes?
I don't understand why you need a READ_ONCE when removing a mutex around 
an assignment
of a parameter passed into a function being assigned to a local variable.

Could you please explain your expectations.
>
>> Signed-off-by: Scott Branden <scott.branden@...adcom.com>
>> ---
>>   lib/test_firmware.c | 26 +++-----------------------
>>   1 file changed, 3 insertions(+), 23 deletions(-)
>>
>> diff --git a/lib/test_firmware.c b/lib/test_firmware.c
>> index 0c7fbcf07ac5..9fee2b93a8d1 100644
>> --- a/lib/test_firmware.c
>> +++ b/lib/test_firmware.c
>> @@ -310,27 +310,13 @@ static int test_dev_config_update_bool(const char *buf, size_t size,
>>   	return ret;
>>   }
>>   
>> -static ssize_t
>> -test_dev_config_show_bool(char *buf,
>> -			  bool config)
>> +static ssize_t test_dev_config_show_bool(char *buf, bool val)
>>   {
>> -	bool val;
>> -
>> -	mutex_lock(&test_fw_mutex);
>> -	val = config;
>> -	mutex_unlock(&test_fw_mutex);
>> -
>>   	return snprintf(buf, PAGE_SIZE, "%d\n", val);
>>   }
>>   
>> -static ssize_t test_dev_config_show_int(char *buf, int cfg)
>> +static ssize_t test_dev_config_show_int(char *buf, int val)
>>   {
>> -	int val;
>> -
>> -	mutex_lock(&test_fw_mutex);
>> -	val = cfg;
>> -	mutex_unlock(&test_fw_mutex);
>> -
>>   	return snprintf(buf, PAGE_SIZE, "%d\n", val);
>>   }
>>   
>> @@ -354,14 +340,8 @@ static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
>>   	return size;
>>   }
>>   
>> -static ssize_t test_dev_config_show_u8(char *buf, u8 cfg)
>> +static ssize_t test_dev_config_show_u8(char *buf, u8 val)
>>   {
>> -	u8 val;
>> -
>> -	mutex_lock(&test_fw_mutex);
>> -	val = cfg;
>> -	mutex_unlock(&test_fw_mutex);
>> -
>>   	return snprintf(buf, PAGE_SIZE, "%u\n", val);
>>   }
>>   
>> -- 
>> 2.17.1
>>