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Subjectlinux-next: build failure after merge of the tip tree (from the drm-intel tree)
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(-)

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,
--
2.8.1



--
Cheers,
Stephen Rothwell

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