tsan: fix false positive related to signal handlers

Users expect synchronization between sigaction and arrival
of the signal. See the test for details.

llvm-svn: 216878

compiler-rt/lib/tsan/rtl/tsan_interceptors.cc

@@ -1685,6 +1685,7 @@ namespace __tsan {
 
 static void CallUserSignalHandler(ThreadState *thr, bool sync, bool sigact,
     int sig, my_siginfo_t *info, void *uctx) {
+  Acquire(thr, 0, (uptr)&sigactions[sig]);
   // Ensure that the handler does not spoil errno.
   const int saved_errno = errno;
   errno = 99;
@@ -1822,6 +1823,7 @@ TSAN_INTERCEPTOR(int, sigaction, int sig, sigaction_t *act, sigaction_t *old) {
     else
       newact.sa_handler = rtl_sighandler;
   }
+  ReleaseStore(thr, pc, (uptr)&sigactions[sig]);
   int res = REAL(sigaction)(sig, &newact, 0);
   return res;
 }

compiler-rt/test/tsan/signal_sync.cc

@@ -0,0 +1,58 @@
+// RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <errno.h>
+
+volatile int X;
+
+static void handler(int sig) {
+  (void)sig;
+  if (X != 42)
+    printf("bad");
+}
+
+static void* thr(void *p) {
+  for (int i = 0; i != 1000; i++)
+    usleep(1000);
+  return 0;
+}
+
+int main() {
+  const int kThreads = 10;
+  pthread_t th[kThreads];
+  for (int i = 0; i < kThreads; i++)
+    pthread_create(&th[i], 0, thr, 0);
+
+  X = 42;
+
+  struct sigaction act = {};
+  act.sa_handler = &handler;
+  if (sigaction(SIGPROF, &act, 0)) {
+    perror("sigaction");
+    exit(1);
+  }
+
+  itimerval t;
+  t.it_value.tv_sec = 0;
+  t.it_value.tv_usec = 10;
+  t.it_interval = t.it_value;
+  if (setitimer(ITIMER_PROF, &t, 0)) {
+    perror("setitimer");
+    exit(1);
+  }
+
+  for (int i = 0; i < kThreads; i++)
+    pthread_join(th[i], 0);
+
+  fprintf(stderr, "DONE\n");
+  return 0;
+}
+
+// CHECK-NOT: WARNING: ThreadSanitizer:
+// CHECK: DONE
+// CHECK-NOT: WARNING: ThreadSanitizer: