[PATCH] Add test case for a known hang in infrun

[Richard Bunt]

The hang occurs when GDB tries to call inferior functions on two
different threads with scheduler-locking turned on. The first call
works fine, with the call to infrun_async(1) causing the
signal_handler to be marked and the event to be handled, but then
the event loop resets the "ready" member to zero, while leaving
infrun_is_async set to 1. As a result, GDB hangs if the user switches
to another thread and calls a second function because calling
infrun_async(1) a second time has no effect, meaning the inferior
call events are never handled.

The added test case provokes the above issue.

gdb/testsuite/ChangeLog:

	* gdb.threads/multiple-successive-infcall.c: New test.
	* gdb.threads/multiple-successive-infcall.exp: New file.
---
 .../gdb.threads/multiple-successive-infcall.c      | 104 +++++++++++++++++++++
 .../gdb.threads/multiple-successive-infcall.exp    |  55 +++++++++++
 2 files changed, 159 insertions(+)
 create mode 100644 gdb/testsuite/gdb.threads/multiple-successive-infcall.c
 create mode 100644 gdb/testsuite/gdb.threads/multiple-successive-infcall.exp

diff --git a/gdb/testsuite/gdb.threads/multiple-successive-infcall.c b/gdb/testsuite/gdb.threads/multiple-successive-infcall.c
new file mode 100644
index 0000000..3010c18
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/multiple-successive-infcall.c
@@ -0,0 +1,104 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2018 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+
+/* This defines the number of threads to spawn.  */
+#define THREADCOUNT 4
+
+/* Global barrier type to control synchronization between threads.  */
+pthread_barrier_t print_barrier;
+/* Define global thread identifiers.  */
+pthread_t threads[THREADCOUNT];
+/* Memory for threads to read from when get_value is called by the
+   debugger.  */
+int thread_ids[THREADCOUNT];
+
+/* Return the argument back, within range [0..THREADCOUNT).
+   This is the function called on the inferiors from the debugger.  */
+int
+get_value (int index)
+{
+  return thread_ids[index];
+}
+
+/* Return the nth Fibonacci number.  */
+unsigned long
+fast_fib (unsigned int n)
+{
+  int a = 0;
+  int b = 1;
+  int t;
+  for (unsigned int i = 0; i < n; ++i)
+    {
+      t = b;
+      b = a + b;
+      a = t;
+    }
+  return a;
+}
+
+/* Encapsulate the synchronization of the threads. Perform a barrier before
+   and after the computation.  */
+void *
+thread_function (void *args)
+{
+  int tid = get_value (*((int *) args));
+  int status = pthread_barrier_wait (&print_barrier);
+  if (status == PTHREAD_BARRIER_SERIAL_THREAD)
+    {
+      printf ("All threads entering compute region\n");
+    }
+  unsigned long result = fast_fib (100);	// testmarker01
+  status = pthread_barrier_wait (&print_barrier);
+  if (status == PTHREAD_BARRIER_SERIAL_THREAD)
+    {
+      printf ("All threads outputting results\n");
+    }
+  pthread_barrier_wait (&print_barrier);
+  printf ("Thread %d Result: %lu\n", tid, result);
+  pthread_exit (NULL);
+}
+
+int
+main (void)
+{
+  int err = pthread_barrier_init (&print_barrier, NULL, THREADCOUNT);
+  // Create the worker threads (main).
+  printf ("Spawning worker threads\n");
+  for (int tid = 0; tid < THREADCOUNT; ++tid)
+    {
+      thread_ids[tid] = tid;
+      err =
+	pthread_create (&threads[tid], NULL, thread_function,
+			(void *) &thread_ids[tid]);
+      if (err)
+	{
+	  fprintf (stderr, "Thread creation failed\n");
+	  return EXIT_FAILURE;
+	}
+    }
+  // Wait for the threads to complete then exit.
+  for (int tid = 0; tid < THREADCOUNT; ++tid)
+    {
+      pthread_join (threads[tid], NULL);
+    }
+  pthread_exit (NULL);
+  return EXIT_SUCCESS;
+}
diff --git a/gdb/testsuite/gdb.threads/multiple-successive-infcall.exp b/gdb/testsuite/gdb.threads/multiple-successive-infcall.exp
new file mode 100644
index 0000000..363f8e0
--- /dev/null
+++ b/gdb/testsuite/gdb.threads/multiple-successive-infcall.exp
@@ -0,0 +1,55 @@
+# Copyright (C) 2018 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+# multiple-successive-infcall.exp -- Test if GDB can invoke functions on
+# multiple inferiors, one after the other.
+
+standard_testfile
+
+if [get_compiler_info] {
+  return -1
+}
+
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" \
+  executable {debug}] != "" } {
+  return -1
+}
+
+clean_restart "${binfile}"
+
+if ![runto_main] then {
+   fail "Can't run to main"
+   return 0
+}
+
+gdb_breakpoint [gdb_get_line_number "testmarker01"]
+gdb_continue_to_breakpoint "testmarker01"
+gdb_test_no_output "set scheduler-locking on"
+gdb_test "show scheduler-locking" \
+  "Mode for locking scheduler during execution is \"on\"."
+
+foreach thread {4 3 2 1}  {
+  gdb_test "thread ${thread}" "Switching to .*"
+  set command "call get_value(0)"
+  gdb_test_multiple "${command}" "${command}" {
+    -re ".*\[\r\n]+${gdb_prompt} $" {
+      pass "Call on inferior returned successfully."
+    }
+    timeout {
+      kfail "gdb/22882" "Call on inferior hung."
+      return 0
+    }
+  }
+}
-- 
2.7.4