patch from Ian Abbot <abbotti@mev.co.uk>:

I think it's probably a bad idea for my amplc_dio200 driver to call
comedi_event() while it's holding a spinlock.  The call to comedi_event
could call a kcomedilib client's callback function, which might do
something that requires the same spinlock, leading to a deadlock.

The attached patch moves the calls to comedi_event() to a safe point
after the spinlock is released.

diff --git a/comedi/drivers/amplc_dio200.c b/comedi/drivers/amplc_dio200.c
index 7a27fbe9e5f774a4e0ebccaa8f9e7ac96f690b5d..ae638e5a929650d6d34a9ce6023e1c4897afbc13 100644 (file)
--- a/comedi/drivers/amplc_dio200.c
+++ b/comedi/drivers/amplc_dio200.c
@@ -364,19 +364,20 @@ dio200_stop_intr(comedi_device *dev, comedi_subdevice *s)
 /*
  * Called to start acquisition for an 'INTERRUPT' subdevice.
  */
-static void
+static int
 dio200_start_intr(comedi_device *dev, comedi_subdevice *s)
 {
        unsigned int n;
        unsigned isn_bits;
        dio200_subdev_intr *subpriv = s->private;
        comedi_cmd *cmd = &s->async->cmd;
+       int retval = 0;
 
        if (!subpriv->continuous && subpriv->stopcount == 0) {
                /* An empty acquisition! */
                s->async->events |= COMEDI_CB_EOA;
-               comedi_event(dev, s, s->async->events);
                subpriv->active = 0;
+               retval = 1;
        } else {
                /* Determine interrupt sources to enable. */
                isn_bits = 0;
@@ -390,6 +391,8 @@ dio200_start_intr(comedi_device *dev, comedi_subdevice *s)
                subpriv->enabled_isns = isn_bits;
                outb(isn_bits, subpriv->iobase);
        }
+
+       return retval;
 }
 
 /*
@@ -401,6 +404,7 @@ dio200_inttrig_start_intr(comedi_device *dev, comedi_subdevice *s,
 {
        dio200_subdev_intr *subpriv;
        unsigned long flags;
+       int event = 0;
 
        if (trignum != 0) return -EINVAL;
 
@@ -409,10 +413,14 @@ dio200_inttrig_start_intr(comedi_device *dev, comedi_subdevice *s,
        comedi_spin_lock_irqsave(&subpriv->spinlock, flags);
        s->async->inttrig = 0;
        if (subpriv->active) {
-               dio200_start_intr(dev, s);
+               event = dio200_start_intr(dev, s);
        }
        comedi_spin_unlock_irqrestore(&subpriv->spinlock, flags);
 
+       if (event) {
+               comedi_event(dev, s, s->async->events);
+       }
+
        return 1;
 }
 
@@ -427,11 +435,13 @@ dio200_handle_read_intr(comedi_device *dev, comedi_subdevice *s)
        unsigned triggered;
        unsigned intstat;
        unsigned cur_enabled;
+       unsigned int oldevents;
        unsigned long flags;
 
        triggered = 0;
 
        comedi_spin_lock_irqsave(&subpriv->spinlock, flags);
+       oldevents = s->async->events;
        /*
         * Collect interrupt sources that have triggered and disable them
         * temporarily.  Loop around until no extra interrupt sources have
@@ -497,15 +507,15 @@ dio200_handle_read_intr(comedi_device *dev, comedi_subdevice *s)
                                                }
                                        }
                                }
-
-                               if (s->async->events) {
-                                       comedi_event(dev, s, s->async->events);
-                               }
                        }
                }
        }
        comedi_spin_unlock_irqrestore(&subpriv->spinlock, flags);
 
+       if (oldevents != s->async->events) {
+               comedi_event(dev, s, s->async->events);
+       }
+
        return (triggered != 0);
 }
 
@@ -630,6 +640,7 @@ dio200_subdev_intr_cmd(comedi_device *dev, comedi_subdevice *s)
        comedi_cmd *cmd = &s->async->cmd;
        dio200_subdev_intr *subpriv = s->private;
        unsigned long flags;
+       int event = 0;
 
        comedi_spin_lock_irqsave(&subpriv->spinlock, flags);
        subpriv->active = 1;
@@ -654,11 +665,15 @@ dio200_subdev_intr_cmd(comedi_device *dev, comedi_subdevice *s)
                break;
        default:
                /* TRIG_NOW */
-               dio200_start_intr(dev, s);
+               event = dio200_start_intr(dev, s);
                break;
        }
        comedi_spin_unlock_irqrestore(&subpriv->spinlock, flags);
 
+       if (event) {
+               comedi_event(dev, s, s->async->events);
+       }
+
        return 0;
 }