[Intel-gfx] [PATCH 2/2] drmtest: Avoid wrong PID/TID after clone races

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Various C library implementations have various races with regards
to caching getpid() or TID inside pthread_kill() implementations.

For example see clone(2) glibc man page and pthread_kill
Bionic C library source.

Work around that by making sure correct PID/TGID and TID values
are retrieved from the kernel when re-raising the signal. It
can be delivered immediately after the clone system call while C
library cached copies have not yet been updated.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 lib/drmtest.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/lib/drmtest.c b/lib/drmtest.c
index dcacd3b..139eb82 100644
--- a/lib/drmtest.c
+++ b/lib/drmtest.c
@@ -43,6 +43,8 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/wait.h>
+#include <sys/types.h>
+#include <sys/syscall.h>
 
 #include "drmtest.h"
 #include "i915_drm.h"
@@ -1473,6 +1475,8 @@ static void igt_atexit_handler(void)
 
 static void fatal_sig_handler(int sig)
 {
+	pid_t pid, tid;
+
 	restore_all_sig_handler();
 
 	/*
@@ -1481,7 +1485,11 @@ static void fatal_sig_handler(int sig)
 	 */
 	call_exit_handlers(sig);
 
-	raise(sig);
+	/* Workaround cached PID and TID races on glibc and Bionic libc. */
+	pid = syscall(SYS_getpid);
+	tid = syscall(SYS_gettid);
+
+	syscall(SYS_tgkill, pid, tid, sig);
 }
 
 /*
-- 
1.8.4.3