[igt-dev] [PATCH i-g-t] lib/igt_core: Reinitialize print mutex in child process

[Zbigniew Kempczyński]

IGT are prone to deadlock in igt_log() in following scenario:

1. Parent process creates additional thread which for example
   is doing endless loop
2. Thread sometimes is logging to console using igt_info().
   This locks and unlocks print_mutex.
3. If in the meantime parent process will spawn it can be
   spawned with print_mutex locked. If in the child process
   it will do igt_info() it will deadlock.

We should reinitialize print_mutex in child process to avoid
use inherited value.

Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
Cc: Petri Latvala <petri.latvala at intel.com>
---
 lib/igt_core.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/igt_core.c b/lib/igt_core.c
index cedd8168..722202ae 100644
--- a/lib/igt_core.c
+++ b/lib/igt_core.c
@@ -2271,6 +2271,8 @@ static void children_exit_handler(int sig)
 		;
 }
 
+static pthread_mutex_t print_mutex = PTHREAD_MUTEX_INITIALIZER;
+
 bool __igt_fork(void)
 {
 	internal_assert(!test_with_subtests || in_subtest,
@@ -2300,6 +2302,7 @@ bool __igt_fork(void)
 		igt_assert(0);
 	case 0:
 		test_child = true;
+		pthread_mutex_init(&print_mutex, NULL);
 		exit_handler_count = 0;
 		reset_helper_process_list();
 		oom_adjust_for_doom();
@@ -2737,8 +2740,6 @@ void igt_vlog(const char *domain, enum igt_log_level level, const char *format,
 		"NONE"
 	};
 
-	static pthread_mutex_t print_mutex = PTHREAD_MUTEX_INITIALIZER;
-
 	assert(format);
 
 #ifdef __GLIBC__
@@ -2747,7 +2748,6 @@ void igt_vlog(const char *domain, enum igt_log_level level, const char *format,
 	program_name = command_str;
 #endif
 
-
 	if (igt_thread_is_main()) {
 		thread_id = strdup("");
 	} else {
@@ -2823,6 +2823,8 @@ out:
 	free(line);
 }
 
+
+
 static const char *timeout_op;
 static void __attribute__((noreturn)) igt_alarm_handler(int signal)
 {
-- 
2.26.0