[PATCH 2/2] staging: comedi: das16: use spin-lock when setting timer

Ian Abbott abbotti at mev.co.uk
Wed Oct 29 17:35:12 UTC 2014

"das16" sets a timer running in `das16_cmd_exec()` and sets
`devpriv->timer_running` to indicate that it is running.  The timer
expiration routine `das16_timer_interrupt()` checks
`devpriv->timer_running` to check whether it needs to reschedule the
timer, but this is not synchronized with `das16_cmd_exec()`.  Since
`das16_cancel()` acquires the `dev->spinlock` spin-lock when clearing
`devpriv->timer_running` and removing the timer from the queue, use the
same spin-lock in `das16_cmd_exec()` and `das16_timer_interrupt()`
around the setting and checking of `devpriv->timer_running`.

Since `das16_interrupt()` (called from `das16_timer_interrupt()`) checks
whether DMA is enabled in the device while holding `dev->spinlock`, and
DMA is enabled by `das16_cmd_exec()` around the time it schedules the
timer, enable the DMA in the device while holding the spin-lock.

Signed-off-by: Ian Abbott <abbotti at mev.co.uk>
 drivers/staging/comedi/drivers/das16.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/drivers/das16.c b/drivers/staging/comedi/drivers/das16.c
index 51c4a58..3d38404 100644
--- a/drivers/staging/comedi/drivers/das16.c
+++ b/drivers/staging/comedi/drivers/das16.c
@@ -593,11 +593,14 @@ static void das16_timer_interrupt(unsigned long arg)
 	struct comedi_device *dev = (struct comedi_device *)arg;
 	struct das16_private_struct *devpriv = dev->private;
+	unsigned long flags;
+	spin_lock_irqsave(&dev->spinlock, flags);
 	if (devpriv->timer_running)
 		mod_timer(&devpriv->timer, jiffies + timer_period());
+	spin_unlock_irqrestore(&dev->spinlock, flags);
 static int das16_ai_check_chanlist(struct comedi_device *dev,
@@ -814,7 +817,8 @@ static int das16_cmd_exec(struct comedi_device *dev, struct comedi_subdevice *s)
-	/*  set up interrupt */
+	/*  set up timer */
+	spin_lock_irqsave(&dev->spinlock, flags);
 	devpriv->timer_running = 1;
 	devpriv->timer.expires = jiffies + timer_period();
@@ -823,6 +827,7 @@ static int das16_cmd_exec(struct comedi_device *dev, struct comedi_subdevice *s)
 	if (devpriv->can_burst)
 		outb(0, dev->iobase + DAS1600_CONV_REG);
+	spin_unlock_irqrestore(&dev->spinlock, flags);
 	return 0;

More information about the devel mailing list