[Intel-gfx] [PATCH] drm/i915: Use rcu to defer freeing of irq_work

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-12-13 10:54:55)
> 
> On 13/12/2017 09:48, Chris Wilson wrote:
> > It is illegal to perform an immediate free of the struct irq_work from
> > inside the irq_work callback (as irq_work_run_list modifies work->flags
> > after execution of the work->func()). As we use the irq_work to
> > coordinate the freeing of the callback from two different softirq paths,
> > we need to defer the kfree from inside our irq_work callback, for which
> > we can use kfree_rcu.
> > 
> > Fixes: 81c0ed21aa91 ("drm/i915/fence: Avoid del_timer_sync() from inside a timer")
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_sw_fence.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
> > index e8ca67a129d2..ac236b88c99c 100644
> > --- a/drivers/gpu/drm/i915/i915_sw_fence.c
> > +++ b/drivers/gpu/drm/i915/i915_sw_fence.c
> > @@ -367,6 +367,7 @@ struct i915_sw_dma_fence_cb {
> >       struct dma_fence *dma;
> >       struct timer_list timer;
> >       struct irq_work work;
> > +     struct rcu_head rcu;
> >   };
> >   
> >   static void timer_i915_sw_fence_wake(struct timer_list *t)
> > @@ -406,7 +407,7 @@ static void irq_i915_sw_fence_work(struct irq_work *wrk)
> >       del_timer_sync(&cb->timer);
> >       dma_fence_put(cb->dma);
> >   
> > -     kfree(cb);
> > +     kfree_rcu(cb, rcu);
> >   }
> >   
> >   int i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
> > 
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Ta, applied. Still hopeful this was more than a one-off on my poor
Braswell.
-Chris