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

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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/  )=-
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