linux-kernel - Re: [PATCH 2/2] mfd: ab8500-core: Return zero in get_register

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Date:   Thu, 25 Oct 2018 11:46:43 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mattias Wallin <mattias.wallin@...ricsson.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/2] mfd: ab8500-core: Return zero in
 get_register_interruptible()

On Thu, Oct 25, 2018 at 09:25:08AM +0100, Lee Jones wrote:
> On Thu, 18 Oct 2018, Dan Carpenter wrote:
> 
> > I just noticed this in review.  The get_register_interruptible() should
> > return zero on success but it instead returns the value that it read.
> > 
> > I looked at all the places that called this directly and they check for
> > negatives and treat greater than or equal to zero as success.  This
> > function is also called as the ->get_register() function pointer.  Some
> > of the callers of that treat all non-zero returns as errors, so it's
> > possible that this bug causes some problems in real life.
> > 
> > I could not find any callers that rely on the current behavior, and this
> > makes the function align with the get_register_interruptible() in
> > ab3100-core.c.
> > 
> > Fixes: 47c1697508f2 ("mfd: Align ab8500 with the abx500 interface")
> > Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> > ---
> >  drivers/mfd/ab8500-core.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/mfd/ab8500-core.c b/drivers/mfd/ab8500-core.c
> > index 30d09d177171..66458a329127 100644
> > --- a/drivers/mfd/ab8500-core.c
> > +++ b/drivers/mfd/ab8500-core.c
> > @@ -252,16 +252,18 @@ static int get_register_interruptible(struct ab8500 *ab8500, u8 bank,
> >  	mutex_lock(&ab8500->lock);
> >  
> >  	ret = ab8500->read(ab8500, addr);
> > -	if (ret < 0)
> > +	if (ret < 0) {
> >  		dev_err(ab8500->dev, "failed to read reg %#x: %d\n",
> >  			addr, ret);
> > -	else
> > -		*value = ret;
> > +		return ret;
> 
> Looks like you just broke the AB8500.
> 


Oh wow.  I screwed up the locking.


> What is it you're trying to achieve here?  Apart from attempting to
> return with the mutex still held, what semantics have you changed?
> 

Sorry that wasn't clear.  Here is the relevant bits from the commit
message.

> > function is also called as the ->get_register() function pointer.  Some
> > of the callers of that treat all non-zero returns as errors, so it's
> > possible that this bug causes some problems in real life.

We're returning positive non-zero values on success instead of zero.
It's definitely a bug, but I'm not sure if it has an impact in real
life.

regards,
dan carpenter