[igt-dev] [PATCH i-g-t v26 11/35] lib/intel_allocator: Separate allocator multiprocess start

["Zbigniew Kempczyński" <zbigniew.kempczynski@intel.com>]

Validating allocator code (leaks and memory overwriting) can be done
with address sanitizer. When allocator is not working in multiprocess
mode it is easy, problems start when fork is in the game. In this
situation we need to separate preparation and starting allocator thread.

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Reported-by: Andrzej Turko <andrzej.turko@linux.intel.com>
Cc: Andrzej Turko <andrzej.turko@linux.intel.com>
Cc: Dominik Grzegorzek <dominik.grzegorzek@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
 lib/intel_allocator.c | 41 ++++++++++++++++++++++++++++++++++-------
 lib/intel_allocator.h |  2 ++
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/lib/intel_allocator.c b/lib/intel_allocator.c
index 9a2bcf2fe..e35d32148 100644
--- a/lib/intel_allocator.c
+++ b/lib/intel_allocator.c
@@ -756,6 +756,38 @@ static void *allocator_thread_loop(void *data)
 	return NULL;
 }
 
+
+/**
+ * __intel_allocator_multiprocess_prepare:
+ *
+ * Prepares allocator infrastructure to work in multiprocess mode.
+ *
+ * Some description is required why prepare/start steps are separated.
+ * When we write the code and we don't use address sanitizer simple
+ * intel_allocator_multiprocess_start() call is enough. With address
+ * sanitizer and using forking we can encounter situation where one
+ * forked child called allocator alloc() (so parent has some poisoned
+ * memory in shadow map), then second fork occurs. Second child will
+ * get poisoned shadow map from parent (there allocator thread reside).
+ * Checking shadow map in this child will report memory leak.
+ *
+ * How to separate initialization steps take a look into api_intel_allocator.c
+ * fork_simple_stress() function.
+ */
+void __intel_allocator_multiprocess_prepare(void)
+{
+	intel_allocator_init();
+
+	multiprocess = true;
+	channel->init(channel);
+}
+
+void __intel_allocator_multiprocess_start(void)
+{
+	pthread_create(&allocator_thread, NULL,
+		       allocator_thread_loop, NULL);
+}
+
 /**
  * intel_allocator_multiprocess_start:
  *
@@ -777,13 +809,8 @@ void intel_allocator_multiprocess_start(void)
 
 	igt_assert_f(child_pid == -1,
 		     "Allocator thread can be spawned only in main IGT process\n");
-	intel_allocator_init();
-
-	multiprocess = true;
-	channel->init(channel);
-
-	pthread_create(&allocator_thread, NULL,
-		       allocator_thread_loop, NULL);
+	__intel_allocator_multiprocess_prepare();
+	__intel_allocator_multiprocess_start();
 }
 
 /**
diff --git a/lib/intel_allocator.h b/lib/intel_allocator.h
index f07663334..f24f7d150 100644
--- a/lib/intel_allocator.h
+++ b/lib/intel_allocator.h
@@ -160,6 +160,8 @@ struct intel_allocator {
 };
 
 void intel_allocator_init(void);
+void __intel_allocator_multiprocess_prepare(void);
+void __intel_allocator_multiprocess_start(void);
 void intel_allocator_multiprocess_start(void);
 void intel_allocator_multiprocess_stop(void);
 
-- 
2.26.0

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