[PATCH 1/8] gdb.threads/{siginfo-thread.c,watchthreads-reorder.c,ia64-sigill.c} races with GDB

[Pedro Alves <palves@redhat.com>]

These three test all spawn a few threads and then send a SIGSTOP to
their parent GDB in order to pause it while the new threads set things
up for the test.  With a GDB patch that changes the inferior thread's
scheduling a bit, I sometimes see:

  FAIL: gdb.threads/siginfo-threads.exp: catch signal 0 (timeout)
  ...
  FAIL: gdb.threads/watchthreads-reorder.exp: reorder1: continue a (timeout)
  ...
  FAIL: gdb.threads/ia64-sigill.exp: continue (timeout)
  ...

The issue is that the test program stops GDB before it had a chance of
processing the new thread's clone event:

  (gdb) PASS: gdb.threads/siginfo-threads.exp: get pid
  continue
  Continuing.
  Stopping GDB PID 21541.
  Waiting till the threads initialize their TIDs.
  FAIL: gdb.threads/siginfo-threads.exp: catch signal 0 (timeout)

On Linux (at least), new threads start stopped, and the debugger must
resume them.  The fix is to make the test program wait for the new
threads to be running before stopping GDB.

gdb/testsuite/
2014-12-26  Pedro Alves  <palves@redhat.com>

	* gdb.threads/ia64-sigill.c (threads_started_barrier): New global.
	(thread_func): Wait on barrier.
	(main): Wait for all threads to start before stopping GDB.
	* gdb.threads/siginfo-threads.c (threads_started_barrier): New
	global.
	(thread1_func, thread2_func): Wait on barrier.
	(main): Wait for all threads to start before stopping GDB.
	* gdb.threads/watchthreads-reorder.c (threads_started_barrier):
	New global.
	(thread1_func, thread2_func): Wait on barrier.
	(main): Wait for all threads to start before stopping GDB.
---
 gdb/testsuite/gdb.threads/ia64-sigill.c          | 11 +++++++++++
 gdb/testsuite/gdb.threads/siginfo-threads.c      | 13 +++++++++++++
 gdb/testsuite/gdb.threads/watchthreads-reorder.c | 13 +++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/gdb/testsuite/gdb.threads/ia64-sigill.c b/gdb/testsuite/gdb.threads/ia64-sigill.c
index 4833e47..a685fb0 100644
--- a/gdb/testsuite/gdb.threads/ia64-sigill.c
+++ b/gdb/testsuite/gdb.threads/ia64-sigill.c
@@ -44,6 +44,8 @@ static pthread_mutex_t thread2_tid_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_
 
 static pthread_mutex_t terminate_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
 
+static pthread_barrier_t threads_started_barrier;
+
 /* Do not use alarm as it would create a ptrace event which would hang up us if
    we are being traced by GDB which we stopped ourselves.  */
 
@@ -78,6 +80,8 @@ thread_func (void *threadno_voidp)
   int threadno = (intptr_t) threadno_voidp;
   int i;
 
+  pthread_barrier_wait (&threads_started_barrier);
+
   switch (threadno)
   {
     case 1:
@@ -272,6 +276,8 @@ main (int argc, char **argv)
 
   timed_mutex_lock (&terminate_mutex);
 
+  pthread_barrier_init (&threads_started_barrier, NULL, 3);
+
   i = pthread_create (&thread1, NULL, thread_func, (void *) (intptr_t) 1);
   assert (i == 0);
 
@@ -298,6 +304,11 @@ main (int argc, char **argv)
 
   atexit (cleanup);
 
+  /* Wait until all threads are seen running.  On Linux (at least),
+     new threads start stopped, and the debugger must resume them.
+     Need to wait for that before stopping GDB.  */
+  pthread_barrier_wait (&threads_started_barrier);
+
   printf ("Stopping GDB PID %lu.\n", (unsigned long) tracer);
 
   if (tracer)
diff --git a/gdb/testsuite/gdb.threads/siginfo-threads.c b/gdb/testsuite/gdb.threads/siginfo-threads.c
index 7aa1ea2..b86df54 100644
--- a/gdb/testsuite/gdb.threads/siginfo-threads.c
+++ b/gdb/testsuite/gdb.threads/siginfo-threads.c
@@ -54,6 +54,8 @@ static int thread2_sigusr2_hit;
 static pthread_mutex_t terminate_mutex
   = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
 
+static pthread_barrier_t threads_started_barrier;
+
 /* Do not use alarm as it would create a ptrace event which would hang
    us up if we are being traced by GDB, which we stopped
    ourselves.  */
@@ -128,6 +130,8 @@ thread1_func (void *unused)
 {
   int i;
 
+  pthread_barrier_wait (&threads_started_barrier);
+
   timed_mutex_lock (&thread1_tid_mutex);
 
   /* THREAD1_TID_MUTEX must be already locked to avoid a race.  */
@@ -163,6 +167,8 @@ thread2_func (void *unused)
 {
   int i;
 
+  pthread_barrier_wait (&threads_started_barrier);
+
   timed_mutex_lock (&thread2_tid_mutex);
 
   /* THREAD2_TID_MUTEX must be already locked to avoid a race.  */
@@ -354,6 +360,8 @@ main (int argc, char **argv)
   assert_perror (errno);
   assert (i == 0);
 
+  pthread_barrier_init (&threads_started_barrier, NULL, 3);
+
   i = pthread_create (&thread1, NULL, thread1_func, NULL);
   assert (i == 0);
 
@@ -380,6 +388,11 @@ main (int argc, char **argv)
 
   atexit (cleanup);
 
+  /* Wait until all threads are seen running.  On Linux (at least),
+     new threads start stopped, and the debugger must resume them.
+     Need to wait for that before stopping GDB.  */
+  pthread_barrier_wait (&threads_started_barrier);
+
   printf ("Stopping GDB PID %lu.\n", (unsigned long) tracer);
 
   if (tracer)
diff --git a/gdb/testsuite/gdb.threads/watchthreads-reorder.c b/gdb/testsuite/gdb.threads/watchthreads-reorder.c
index 315104a..05b200c 100644
--- a/gdb/testsuite/gdb.threads/watchthreads-reorder.c
+++ b/gdb/testsuite/gdb.threads/watchthreads-reorder.c
@@ -44,6 +44,8 @@ static pthread_mutex_t thread2_tid_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_
 
 static pthread_mutex_t terminate_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
 
+static pthread_barrier_t threads_started_barrier;
+
 /* These variables must have lower in-memory addresses than thread1_rwatch and
    thread2_rwatch so that they take their watchpoint slots.  */
 
@@ -87,6 +89,8 @@ thread1_func (void *unused)
   int i;
   volatile int rwatch_store;
 
+  pthread_barrier_wait (&threads_started_barrier);
+
   timed_mutex_lock (&thread1_tid_mutex);
 
   /* THREAD1_TID_MUTEX must be already locked to avoid race.  */
@@ -113,6 +117,8 @@ thread2_func (void *unused)
   int i;
   volatile int rwatch_store;
 
+  pthread_barrier_wait (&threads_started_barrier);
+
   timed_mutex_lock (&thread2_tid_mutex);
 
   /* THREAD2_TID_MUTEX must be already locked to avoid race.  */
@@ -279,6 +285,8 @@ main (int argc, char **argv)
 
   timed_mutex_lock (&terminate_mutex);
 
+  pthread_barrier_init (&threads_started_barrier, NULL, 3);
+
   i = pthread_create (&thread1, NULL, thread1_func, NULL);
   assert (i == 0);
 
@@ -305,6 +313,11 @@ main (int argc, char **argv)
 
   atexit (cleanup);
 
+  /* Wait until all threads are seen running.  On Linux (at least),
+     new threads start stopped, and the debugger must resume them.
+     Need to wait for that before stopping GDB.  */
+  pthread_barrier_wait (&threads_started_barrier);
+
   printf ("Stopping GDB PID %lu.\n", (unsigned long) tracer);
 
   if (tracer)
-- 
1.9.3