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

[Ian Abbott]

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@xxxxxxxxx>
> > Cc: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: devel@xxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxx> )=-
-=(                          Web: http://www.mev.co.uk/  )=-