Re: [PATCH] test_firmware: remove unnecessary test_fw_mutex in test_dev_config_show_xxx

From: Scott Branden <scott.branden@broadcom.com>
To: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	David Brown <david.brown@linaro.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Shuah Khan <shuah@kernel.org>,
	bjorn.andersson@linaro.org,
	Shuah Khan <skhan@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-fsdevel@vger.kernel.org,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
	Olof Johansson <olof@lixom.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Colin Ian King <colin.king@canonical.com>,
	Takashi Iwai <tiwai@suse.de>,
	linux-kselftest@vger.kernel.org, Andy Gross <agross@kernel.org>
Subject: Re: [PATCH] test_firmware: remove unnecessary test_fw_mutex in test_dev_config_show_xxx
Date: Wed, 15 Apr 2020 09:28:18 -0700	[thread overview]
Message-ID: <e2b95fde-0ab7-c0d1-2c64-cceffc458673@broadcom.com> (raw)
In-Reply-To: <202004142010.C0847F5@keescook>

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@broadcom.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
>>