linux-kernel - Re: [PATCH 26/31] staging/comedi/das16: Make timer initialization unconditional

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Date:   Fri, 1 Sep 2017 10:38:47 +0100
From:   Ian Abbott <abbotti@....co.uk>
To:     Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     H Hartley Sweeten <hsweeten@...ionengravers.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 26/31] staging/comedi/das16: Make timer initialization
 unconditional

On 01/09/17 10:29, Ian Abbott wrote:
> On 01/09/17 00:29, Kees Cook wrote:
>> With timer initialization made unconditional, there is no reason to
>> make del_timer_sync() calls conditionally, there by removing the test
>> of the .data field.
>>
>> Cc: Ian Abbott <abbotti@....co.uk>
>> Cc: H Hartley Sweeten <hsweeten@...ionengravers.com>
>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>> Cc: devel@...verdev.osuosl.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>   drivers/staging/comedi/drivers/das16.c | 9 +++------
>>   1 file changed, 3 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/staging/comedi/drivers/das16.c 
>> b/drivers/staging/comedi/drivers/das16.c
>> index 5d157951f63f..4514179b2007 100644
>> --- a/drivers/staging/comedi/drivers/das16.c
>> +++ b/drivers/staging/comedi/drivers/das16.c
>> @@ -941,10 +941,8 @@ static void das16_alloc_dma(struct comedi_device 
>> *dev, unsigned int dma_chan)
>>       /* DMA uses two buffers */
>>       devpriv->dma = comedi_isadma_alloc(dev, 2, dma_chan, dma_chan,
>>                          DAS16_DMA_SIZE, COMEDI_ISADMA_READ);
>> -    if (devpriv->dma) {
>> -        setup_timer(&devpriv->timer, das16_timer_interrupt,
>> -                (unsigned long)dev);
>> -    }
>> +    setup_timer(&devpriv->timer, das16_timer_interrupt,
>> +            (unsigned long)dev);
>>   }
> 
> das16_alloc_dma() returns before the call to comedi_isadma_alloc() if 
> the dma_chan parameter is not one of the values 1 or 3, so setup_timer() 
> will not be called in that case.
> 
>>   static void das16_free_dma(struct comedi_device *dev)
>> @@ -952,8 +950,7 @@ static void das16_free_dma(struct comedi_device *dev)
>>       struct das16_private_struct *devpriv = dev->private;
>>       if (devpriv) {
>> -        if (devpriv->timer.data)
>> -            del_timer_sync(&devpriv->timer);
>> +        del_timer_sync(&devpriv->timer);
> 
> If setup_timer() has not been called (see remark above), this change 
> will break.
> 
>>           comedi_isadma_free(devpriv->dma);
>>       }
>>   }
>>

If you want to avoid testing devpriv->timer.data for some reason, you 
could make the calls to setup_timer() and del_timer_sync() depend on 
devpriv->dma.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-