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drm/i915: Add compiler barrier to wait_for

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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@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423113754.28424-2-mika.kuoppala@linux.intel.com
This commit is contained in:
Mika Kuoppala 2018-04-23 14:37:54 +03:00
parent 3085982c6b
commit 1c3c1dc66a
1 changed files with 4 additions and 0 deletions
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4
drivers/gpu/drm/i915/intel_drv.h
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@ -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; \