linux-kernel - Re: [PATCH 1/2] soundwire: bus: Prevent infinite loop in sdw_ch_mask_to

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Message-ID: <2d1f1bc1-afaa-b1f4-1a93-df1bfa00405b@opensource.cirrus.com>
Date:   Fri, 3 Feb 2023 16:18:30 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <sanyog.r.kale@...el.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH 1/2] soundwire: bus: Prevent infinite loop in
 sdw_ch_mask_to_ch()

On 03/02/2023 14:35, Pierre-Louis Bossart wrote:
> 
> 
> On 2/2/23 09:42, Richard Fitzgerald wrote:
>> Define the ch_mask argument of sdw_ch_mask_to_ch() as an unsigned
>> so that the shift right is guaranteed to eventually make the
>> value of ch_mask==0.
>>
>> Previously ch_mask was defined as a signed int, but a right
>> shift of a signed value preserves the sign bit. So if the sign
>> bit was 1, ch_mask would never become 0 and the for loop would
>> be infinite.
>> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
>> ---
>>   drivers/soundwire/bus.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
>> index 7631ef5e71fb..28bedc919b78 100644
>> --- a/drivers/soundwire/bus.h
>> +++ b/drivers/soundwire/bus.h
>> @@ -160,7 +160,7 @@ int sdw_fill_msg(struct sdw_msg *msg, struct sdw_slave *slave,
>>   		 u32 addr, size_t count, u16 dev_num, u8 flags, u8 *buf);
>>   
>>   /* Retrieve and return channel count from channel mask */
>> -static inline int sdw_ch_mask_to_ch(int ch_mask)
>> +static inline int sdw_ch_mask_to_ch(unsigned int ch_mask)
>>   {
>>   	int c = 0;
>>   
> 
> This patch1 is fine, but you remove this function in patch2, so is this
> patch needed at all?
> 
> -/* Retrieve and return channel count from channel mask */
> -static inline int sdw_ch_mask_to_ch(unsigned int ch_mask)
> -{
> -	int c = 0;
> -
> -	for (c = 0; ch_mask; ch_mask >>= 1)
> -		c += ch_mask & 1;
> -
> -	return c;
> -}
> -

I'm happy to squash them, I did it in two steps so it didn't get
overlooked that there's a bugfix happening.