We need to be careful to not let compiler evaluate
the expiration and the operation on it's terms.
Document and enforce that COND will be evaluated
before checking timeout expiration.
Suggested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_drv.h | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 33ff2638c92b..58868b93d2a0 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -56,6 +56,8 @@
for (;;) { \
const bool expired__ = ktime_after(ktime_get_raw(), end__); \
OP; \
+ /* Guarantee COND check prior to timeout */ \
+ barrier(); \
if (COND) { \
ret__ = 0; \
break; \
@@ -96,6 +98,8 @@
u64 now = local_clock(); \
if (!(ATOMIC)) \
preempt_enable(); \
+ /* Guarantee COND check prior to timeout */ \
+ barrier(); \
if (COND) { \
ret = 0; \
break; \
--
2.14.1
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