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

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Date:   Wed, 15 Mar 2023 19:13:10 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        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 03-02-23, 16:18, Richard Fitzgerald wrote:
> 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.

I think this case is fine to squash and send as a single patch while
documenting that we are fixing the bug in the log

Thanks
-- 
~Vinod