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

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Date:   Fri, 1 Sep 2017 10:29:56 +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 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);
>   	}
>   }
> 


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