[igt-dev] [PATCH i-g-t] tests/i915/sysfs_heartbeat_interval: Avoid signal delivery race

[Zbigniew Kempczyński]

As Petri noticed there's signal delivery race which might lead to
situation when two children send SIGALRM to master process not in
the same time. Signal from first child just awake master process
which reinstalls previous signal handler. Second signal is then
handled by default handler so we got process exit and failure.
Lets move signal reinstall to moment when children will just exit.

Allocator warning which notices there's existing ipc queue is
then an effect, not the reason. Unfortunately multiprocess start/stop
were called in the test, not in the fixture, so test failure doesn't
call multiprocess stop at all (and we see there's dangling queue).

Deeper look to client() implementation allows to remove multiprocess
allocator dependency. Function runs in its own separated context
so we don't need to arbitrate and just call intel_allocator_init()
to become standalone allocator.

Fixes: https://gitlab.freedesktop.org/drm/intel/-/issues/4055

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
Cc: Petri Latvala <petri.latvala at intel.com>
---
 tests/i915/sysfs_heartbeat_interval.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/tests/i915/sysfs_heartbeat_interval.c b/tests/i915/sysfs_heartbeat_interval.c
index bc8d1b3c0a..8cebf6270f 100644
--- a/tests/i915/sysfs_heartbeat_interval.c
+++ b/tests/i915/sysfs_heartbeat_interval.c
@@ -364,8 +364,6 @@ static void __test_mixed(int i915, int engine,
 	 * terminate the hog leaving the good client to run.
 	 */
 
-	intel_allocator_multiprocess_start();
-
 	igt_assert(igt_sysfs_scanf(engine, ATTR, "%u", &saved) == 1);
 	igt_debug("Initial %s:%u\n", ATTR, saved);
 	gem_quiescent_gpu(i915);
@@ -375,22 +373,25 @@ static void __test_mixed(int i915, int engine,
 
 	set_heartbeat(engine, heartbeat);
 
-	igt_fork(child, 1) /* good client */
+	igt_fork(child, 1) /* good client */ {
+		intel_allocator_init();
 		client(i915, engine, shared, good, 1);
-	igt_fork(child, 1) /* bad client */
+	}
+	igt_fork(child, 1) /* bad client */ {
+		intel_allocator_init();
 		client(i915, engine, shared, bad, -EIO);
+	}
 
 	old = signal(SIGALRM, sighandler);
 	sleep(duration);
-	signal(SIGALRM, old);
 
 	*shared = true;
 	igt_waitchildren();
 	munmap(shared, 4096);
+	signal(SIGALRM, old);
 
 	gem_quiescent_gpu(i915);
 	set_heartbeat(engine, saved);
-	intel_allocator_multiprocess_stop();
 }
 
 static void test_mixed(int i915, int engine)
-- 
2.32.0