[Piglit] [PATCH 1/3] Make atomic counter tests more robust against race conditions.

Kenneth Graunke kenneth at whitecape.org
Wed Oct 21 01:11:25 PDT 2015

From: Chris Wilson <chris at chris-wilson.co.uk>

Drivers with synchronization bugs could generate errors such as:

Probe value at (0)
  Expected: 0x00000001
  Observed: 0x00000001

This is because the initial comparison and the print statement access
the buffer at different times, leading to the following scenario.

1. Comparison reads wrong value from the buffer (test properly fails).
2. Right value finally lands in buffer.
3. Error message prints the current value...which is the not the value
   used by the comparison.  Instead, it's the expected value, so the
   message makes no sense.

[Ken imported this patch from Chris Wilson's Bugzilla comment linked
 below and wrote a commit message.]

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91298
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
 tests/spec/arb_shader_atomic_counters/common.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

Chris, I made you the author on this patch since it's your code.
It didn't look like a patch ever hit the mailing list, so I went
ahead and put one together...

diff --git a/tests/spec/arb_shader_atomic_counters/common.c b/tests/spec/arb_shader_atomic_counters/common.c
index b966009..c732699 100644
--- a/tests/spec/arb_shader_atomic_counters/common.c
+++ b/tests/spec/arb_shader_atomic_counters/common.c
@@ -35,6 +35,7 @@ atomic_counters_probe_buffer(unsigned base, unsigned count,
         uint32_t *p = glMapBufferRange(
                 GL_ATOMIC_COUNTER_BUFFER, base * sizeof(uint32_t),
                 count * sizeof(uint32_t), GL_MAP_READ_BIT);
+        bool pass = true;
         unsigned i;
         if (!p) {
@@ -43,17 +44,18 @@ atomic_counters_probe_buffer(unsigned base, unsigned count,
         for (i = 0; i < count; ++i) {
-                if (p[i] != expected[i]) {
+                uint32_t found = p[i];
+                if (found != expected[i]) {
                         printf("Probe value at (%i)\n", i);
                         printf("  Expected: 0x%08x\n", expected[i]);
-                        printf("  Observed: 0x%08x\n", p[i]);
-                        glUnmapBuffer(GL_ATOMIC_COUNTER_BUFFER);
-                        return false;
+                        printf("  Observed: 0x%08x\n", found);
+                        pass = false;
+                        break;
-        return true;
+        return pass;

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