Re: [PATCH] drm/i915: Don't del_timer_sync uninitialized timer

[Chris Wilson <chris@chris-wilson.co.uk>]

On Sat, Mar 15, 2014 at 11:30:18AM -0700, Ben Widawsky wrote:
> On Sat, Mar 15, 2014 at 03:20:23PM +0000, Chris Wilson wrote:
> > On Sat, Mar 15, 2014 at 12:47:22PM +0100, Daniel Vetter wrote:
> > > On Fri, Mar 14, 2014 at 05:21:36PM -0700, Ben Widawsky wrote:
> > > > Broken by:
> > > > commit 0294ae7b44bba7ab0d4cef9a8736287f38bdb4fd
> > > > Author: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Date:   Thu Mar 13 12:00:29 2014 +0000
> > > > 
> > > >     drm/i915: Consolidate forcewake resetting to a single function
> > > > 
> > > > Cc: Chris Wilson <chris@chris-wilson.co.uk>
> > > > Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> > > > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_uncore.c | 6 +++---
> > > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> > > > index e6bb421..7e55ceb 100644
> > > > --- a/drivers/gpu/drm/i915/intel_uncore.c
> > > > +++ b/drivers/gpu/drm/i915/intel_uncore.c
> > > > @@ -362,6 +362,9 @@ void intel_uncore_early_sanitize(struct drm_device *dev)
> > > >  {
> > > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > > >  
> > > > +	setup_timer(&dev_priv->uncore.force_wake_timer,
> > > > +		    gen6_force_wake_timer, (unsigned long)dev_priv);
> > > 
> > > We call early_sanitize also from our resume code, so this will now
> > > re-setup the timer again. We generally don't do that since if we ever leak
> > > the timer to here in an enabled state it causes havoc.
> > 
> > Gah, really? intel_uncore_early_init()! There must be a clean way to
> > break this up.
> > -Chris
> 
> At least in the code base I was looking at, we currently do this also,
> so I didn't think this was any worse.
> 
> With lockdep turned on, the module will not even load, so please either
> revert the original, or merge this.

I think we can just:

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index a62ff21..c9fcc20 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -317,9 +317,10 @@ static void intel_uncore_forcewake_reset(struct drm_device *dev, bool restore)
 {
        struct drm_i915_private *dev_priv = dev->dev_private;
        unsigned long irqflags;
-       int pending;
+       int pending = 0;
 
-       pending = del_timer_sync(&dev_priv->uncore.force_wake_timer);
+       if (dev_priv->uncore.force_wake_timer.function)
+               pending = del_timer_sync(&dev_priv->uncore.force_wake_timer);
 
        /* Hold uncore.lock across reset to prevent any register access
         * with forcewake not set correctly

i.e.

-       del_timer_sync(&dev_priv->uncore.force_wake_timer);
+       if (dev_priv->uncore.force_wake_timer.function)
+               del_timer_sync(&dev_priv->uncore.force_wake_timer);

-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre