| Message ID | 20160705135303.6a1bc80a@canb.auug.org.au (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jul 05, 2016 at 01:53:03PM +1000, Stephen Rothwell wrote: > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index d3502c0603e5..1f91f187b2a8 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -3290,7 +3290,7 @@ i915_gem_retire_work_handler(struct work_struct *work) > * We do not need to do this test under locking as in the worst-case > * we queue the retire worker once too often. > */ > - if (lockless_dereference(dev_priv->gt.awake)) > + if (/*lockless_dereference*/(dev_priv->gt.awake)) > queue_delayed_work(dev_priv->wq, > &dev_priv->gt.retire_work, > round_jiffies_up_relative(HZ)); > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c > index f6de8dd567a2..2c1926418691 100644 > --- a/drivers/gpu/drm/i915/i915_irq.c > +++ b/drivers/gpu/drm/i915/i915_irq.c > @@ -3095,7 +3095,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work) > if (!i915.enable_hangcheck) > return; > > - if (!lockless_dereference(dev_priv->gt.awake)) > + if (!/*lockless_dereference*/(dev_priv->gt.awake)) > return; > > /* As enabling the GPU requires fairly extensive mmio access, Right, neither case appears to include a data dependency and thus lockless_dereference() seems misguided.
On Tue, Jul 05, 2016 at 10:25:12AM +0200, Peter Zijlstra wrote: > On Tue, Jul 05, 2016 at 01:53:03PM +1000, Stephen Rothwell wrote: > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > > index d3502c0603e5..1f91f187b2a8 100644 > > --- a/drivers/gpu/drm/i915/i915_gem.c > > +++ b/drivers/gpu/drm/i915/i915_gem.c > > @@ -3290,7 +3290,7 @@ i915_gem_retire_work_handler(struct work_struct *work) > > * We do not need to do this test under locking as in the worst-case > > * we queue the retire worker once too often. > > */ > > - if (lockless_dereference(dev_priv->gt.awake)) > > + if (/*lockless_dereference*/(dev_priv->gt.awake)) > > queue_delayed_work(dev_priv->wq, > > &dev_priv->gt.retire_work, > > round_jiffies_up_relative(HZ)); > > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c > > index f6de8dd567a2..2c1926418691 100644 > > --- a/drivers/gpu/drm/i915/i915_irq.c > > +++ b/drivers/gpu/drm/i915/i915_irq.c > > @@ -3095,7 +3095,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work) > > if (!i915.enable_hangcheck) > > return; > > > > - if (!lockless_dereference(dev_priv->gt.awake)) > > + if (!/*lockless_dereference*/(dev_priv->gt.awake)) > > return; > > > > /* As enabling the GPU requires fairly extensive mmio access, > > Right, neither case appears to include a data dependency and thus > lockless_dereference() seems misguided. Agreed! At first glance, this code wants READ_ONCE() rather than lockless_dereference(). Thanx, Paul
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index d3502c0603e5..1f91f187b2a8 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -3290,7 +3290,7 @@ i915_gem_retire_work_handler(struct work_struct *work) * We do not need to do this test under locking as in the worst-case * we queue the retire worker once too often. */ - if (lockless_dereference(dev_priv->gt.awake)) + if (/*lockless_dereference*/(dev_priv->gt.awake)) queue_delayed_work(dev_priv->wq, &dev_priv->gt.retire_work, round_jiffies_up_relative(HZ)); diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c index f6de8dd567a2..2c1926418691 100644 --- a/drivers/gpu/drm/i915/i915_irq.c +++ b/drivers/gpu/drm/i915/i915_irq.c @@ -3095,7 +3095,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work) if (!i915.enable_hangcheck) return; - if (!lockless_dereference(dev_priv->gt.awake)) + if (!/*lockless_dereference*/(dev_priv->gt.awake)) return; /* As enabling the GPU requires fairly extensive mmio access,
Hi all, After merging the tip tree, today's linux-next build (x86_64 allmodconfig) failed like this: In file included from include/uapi/linux/stddef.h:1:0, from include/linux/stddef.h:4, from include/uapi/linux/posix_types.h:4, from include/uapi/linux/types.h:13, from include/linux/types.h:5, from include/linux/sysrq.h:18, from drivers/gpu/drm/i915/i915_irq.c:31: drivers/gpu/drm/i915/i915_irq.c: In function 'i915_hangcheck_elapsed': include/linux/compiler.h:542:50: error: incompatible types when initializing type 'const void * const' using type 'bool {aka _Bool}' __maybe_unused const void * const _________p2 = _________p1; \ ^ drivers/gpu/drm/i915/i915_irq.c:3098:7: note: in expansion of macro 'lockless_dereference' if (!lockless_dereference(dev_priv->gt.awake)) ^ Caused by commit 67d97da34917 ("drm/i915: Only start retire worker when idle") from the drm-intel tree interacting with commit 331b6d8c7afc ("locking/barriers: Validate lockless_dereference() is used on a pointer type") from the tip tree. From include/linux/compiler.h: * lockless_dereference() - safely load a pointer for later dereference * @p: The pointer to load It looks like lockless_dererence() has been used incorrectly in the drm-intel tree commit since its argument must be a pointer to be dererenced later. The same thing is done in drivers/gpu/drm/i915/i915_gem.c as well. I have applied the following hack patch for now, but this needs to be fixed properly. From: Stephen Rothwell <sfr@canb.auug.org.au> Date: Tue, 5 Jul 2016 13:44:39 +1000 Subject: [PATCH] drm/i915: hack around bad use of lockless_dereference() Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> --- drivers/gpu/drm/i915/i915_gem.c | 2 +- drivers/gpu/drm/i915/i915_irq.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)