linux-kernel - Re: [PATCH] iio: ensure ret is initialized to zero before entering do loop

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Date:   Wed, 7 Sep 2016 20:10:51 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Colin King <colin.king@...onical.com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: ensure ret is initialized to zero before entering do
 loop

On 06/09/16 18:10, Brian Norris wrote:
> Hi,
> 
> On Mon, Sep 05, 2016 at 09:03:26PM +0100, Jonathan Cameron wrote:
>> On 05/09/16 15:39, Colin King wrote:
>>> From: Colin Ian King <colin.king@...onical.com>
>>>
>>> A recent fix to iio_buffer_read_first_n_outer removed ret from being set by
>>> a return from wait_event_interruptible and also added a continue in a loop
>>> which causes the variable ret to not be set when it reaches the end of the
>>> loop.  Fix this by initializing ret to zero.
>>>
>>> Also remove extraneous white space at the end of the loop.
>>>
>>> Fixes: fcf68f3c0bb2a5 ("fix sched WARNING "do not call blocking ops when !TASK_RUNNING")
> 
> Not that it really matters, but if the commit is still going to be
> amended at all, the subject was "iio: fix ...", not just "fix ...".
> Definitely not important though.
> 
>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>> Good find.  Strange that got through 0-day without a warning...
>>
>> Cc'd Brian as author of the fix this is fixing.
>> Brian can you sanity check this patch as well.
> 
> Indeed, looks fine, and works fine:
> 
> Tested-by: Brian Norris <briannorris@...omium.org>
> Reviewed-by: Brian Norris <briannorris@...omium.org>
Hi Brian,

Thanks for checking this out.  Unfortunately I've already
applied it to fixes-togreg branch of iio.git which is strictly
non rebasing so we'll have to rely on the email trace rather
than git history to pick up on your tested by /reviewed by!

Made me more comfortable sending the pull request to Greg
though so thanks!

Jonathan
> 
> Thanks for the fix Colin, and sorry for not noticing that error :(
> 
>> Applied to the fixes-togreg branch of iio.git and marked for stable.
>> Ah well, another one for the statistics on stable patches that introduce bugs while
>> fixing other bugs.
>>
>> Pretty unlikely this will be hit I think, but in theory you never know.
>>
>> Jonathan
>>> ---
>>>  drivers/iio/industrialio-buffer.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
>>> index 49bf9c5..158aaf4 100644
>>> --- a/drivers/iio/industrialio-buffer.c
>>> +++ b/drivers/iio/industrialio-buffer.c
>>> @@ -110,7 +110,7 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
>>>  	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>>>  	size_t datum_size;
>>>  	size_t to_wait;
>>> -	int ret;
>>> +	int ret = 0;
>>>  
>>>  	if (!indio_dev->info)
>>>  		return -ENODEV;
>>> @@ -153,7 +153,7 @@ ssize_t iio_buffer_read_first_n_outer(struct file *filp, char __user *buf,
>>>  		ret = rb->access->read_first_n(rb, n, buf);
>>>  		if (ret == 0 && (filp->f_flags & O_NONBLOCK))
>>>  			ret = -EAGAIN;
>>> -	 } while (ret == 0);
>>> +	} while (ret == 0);
> 
> Personally, I avoided the temptation to fix the whitespace error in a
> bugfix patch. But this does scratch my itch :)
> 
> Brian
> 
>>>  	remove_wait_queue(&rb->pollq, &wait);
>>>  
>>>  	return ret;
>>>
>>
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