[PATCH 3/3] Fix PR 19461: strange "info thread" behavior in non-stop

[Pedro Alves <palves at redhat dot com>]

If you have "set follow-fork child" set, then if you do "info threads"
right after a fork, and before the child reports any other event to
GDB core, you'll see:

(gdb) info threads
  Id   Target Id         Frame
* 1.1  Thread 0x7ffff7fc1740 (LWP 31875) "fork-plus-threa" (running)
  2.1  process 31879 "fork-plus-threa" Selected thread is running.
(gdb)

The "Selected thread is running." bit is a bogus error.  That was GDB
trying to fetch the current frame of thread 2.1, because the external
runnning state is "stopped", and then throwing an error because the
thread is actually running.

This actually affects all-stop + schedule-multiple as well.

The problem here is that on a fork event, GDB doesn't update the
external parent/child running states.

New comprehensive test included.  The "kill inferior 1" / "kill
inferior 2" bits also trip on PR gdb/19494 (hang killing unfollowed
fork children), which was fixed by the previous patch.

gdb/ChangeLog:
2016-01-19  Pedro Alves  <palves@redhat.com>

	PR threads/19461
	* infrun.c (handle_inferior_event_1) <fork/vfork>: Update
	parent/child running states.

gdb/testsuite/ChangeLog:
2016-01-19  Pedro Alves  <palves@redhat.com>

	PR threads/19461
	* gdb.base/fork-running-state.c: New file.
	* gdb.base/fork-running-state.exp: New file.
---
 gdb/infrun.c                                  |  11 ++
 gdb/testsuite/gdb.base/fork-running-state.c   |  83 +++++++++++++
 gdb/testsuite/gdb.base/fork-running-state.exp | 163 ++++++++++++++++++++++++++
 3 files changed, 257 insertions(+)
 create mode 100644 gdb/testsuite/gdb.base/fork-running-state.c
 create mode 100644 gdb/testsuite/gdb.base/fork-running-state.exp

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 33981d2..15210c9 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -5198,6 +5198,17 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
 	  parent = ecs->ptid;
 	  child = ecs->ws.value.related_pid;
 
+	  /* At this point, the parent is marked running, and the
+	     child is marked stopped.  */
+
+	  /* If not resuming the parent, mark it stopped.  */
+	  if (follow_child && !detach_fork && !non_stop && !sched_multi)
+	    set_running (parent, 0);
+
+	  /* If resuming the child, mark it running.  */
+	  if (follow_child || (!detach_fork && (non_stop || sched_multi)))
+	    set_running (child, 1);
+
 	  /* In non-stop mode, also resume the other branch.  */
 	  if (!detach_fork && (non_stop
 			       || (sched_multi && target_is_non_stop_p ())))
diff --git a/gdb/testsuite/gdb.base/fork-running-state.c b/gdb/testsuite/gdb.base/fork-running-state.c
new file mode 100644
index 0000000..c7103fd
--- /dev/null
+++ b/gdb/testsuite/gdb.base/fork-running-state.c
@@ -0,0 +1,83 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2015-2016 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 <unistd.h>
+#include <stdio.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+int save_parent;
+
+/* The fork child.  Just runs forever.  */
+
+static int
+fork_child (void)
+{
+  while (1)
+    {
+      sleep (1);
+
+      /* Exit if GDB kills the parent.  */
+      if (getppid () != save_parent)
+	break;
+      if (kill (getppid (), 0) != 0)
+	break;
+    }
+
+  return 0;
+}
+
+/* The fork parent.  Just runs forever waiting for the child to
+   exit.  */
+
+static int
+fork_parent (void)
+{
+  if (wait (NULL) == -1)
+    {
+      perror ("wait");
+      return 1;
+    }
+
+  return 0;
+}
+
+int
+main (void)
+{
+  pid_t pid;
+
+  save_parent = getpid ();
+
+  /* Don't run forever.  */
+  alarm (180);
+
+  /* The parent and child should basically run forever without
+     tripping on any debug event.  We want to check that GDB updates
+     the parent and child running states correctly right after the
+     fork.  */
+  pid = fork ();
+  if (pid > 0)
+    return fork_parent ();
+  else if (pid == 0)
+    return fork_child ();
+  else
+    {
+      perror ("fork");
+      return 1;
+    }
+}
diff --git a/gdb/testsuite/gdb.base/fork-running-state.exp b/gdb/testsuite/gdb.base/fork-running-state.exp
new file mode 100644
index 0000000..be81be6
--- /dev/null
+++ b/gdb/testsuite/gdb.base/fork-running-state.exp
@@ -0,0 +1,163 @@
+# Copyright (C) 2016 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/>.
+
+# Regression test for PR threads/19461 (strange "info thread" behavior
+# in non-stop).  GDB used to miss updating the parent/child running
+# states after a fork.
+
+standard_testfile
+
+# The test proper.
+
+proc do_test { detach_on_fork follow_fork non_stop schedule_multiple } {
+    global GDBFLAGS
+    global srcfile testfile
+    global gdb_prompt
+
+    save_vars { GDBFLAGS } {
+	append GDBFLAGS " -ex \"set non-stop $non_stop\""
+
+	if {[prepare_for_testing "failed to prepare" \
+		 $testfile $srcfile {debug}] == -1} {
+	    return -1
+	}
+    }
+
+    if ![runto_main] then {
+	fail "Can't run to main"
+	return 0
+    }
+
+    # If debugging with target remote, check whether the all-stop
+    # variant of the RSP is being used.  If so, we can't run the
+    # all-stop tests.
+    if { [target_info exists gdb_protocol]
+	 && ([target_info gdb_protocol] == "remote"
+	     || [target_info gdb_protocol] == "extended-remote")} {
+
+	set test "maint show target-non-stop"
+	gdb_test_multiple "maint show target-non-stop" $test {
+	    -re "(is|currently) on.*$gdb_prompt $" {
+	    }
+	    -re "(is|currently) off.*$gdb_prompt $" {
+		unsupported "can't issue info threads while target is running"
+		return 0
+	    }
+	}
+    }
+
+    # We want to catch "[New inferior ...]" below, to avoid sleeping.
+    if {$detach_on_fork == "off" || $follow_fork == "child"} {
+	gdb_test_no_output "set print inferior-events on"
+    }
+
+    gdb_test_no_output "set detach-on-fork $detach_on_fork"
+
+    gdb_test_no_output "set follow-fork $follow_fork"
+    if {$non_stop == "off"} {
+	gdb_test_no_output "set schedule-multiple $schedule_multiple"
+    }
+
+    set test "continue &"
+    gdb_test_multiple $test $test {
+	-re "$gdb_prompt " {
+	    pass $test
+	}
+    }
+
+    if {$detach_on_fork == "off" || $follow_fork == "child"} {
+	set test "fork child appears"
+	gdb_test_multiple "" $test {
+	    -re "\\\[New inferior " {
+		pass $test
+	    }
+	}
+    } else {
+	# All we can do is wait a little bit for the parent to fork.
+	sleep 1
+    }
+
+    set not_nl "\[^\r\n\]*"
+
+    if {$detach_on_fork == "on" && $non_stop == "on" && $follow_fork == "child"} {
+	gdb_test "info threads" \
+	    "  2.1 ${not_nl}\\\(running\\\).*No selected thread.*"
+    } elseif {$detach_on_fork == "on" && $follow_fork == "child"} {
+	gdb_test "info threads" \
+	    "\\\* 2.1 ${not_nl}\\\(running\\\)"
+    } elseif {$detach_on_fork == "on"} {
+	gdb_test "info threads" \
+	    "\\\* 1 ${not_nl}\\\(running\\\)"
+    } elseif {$non_stop == "on"
+	      || ($schedule_multiple == "on" && $follow_fork == "parent")} {
+	# Both parent and child should be marked running, and the
+	# parent should be selected.
+	gdb_test "info threads" \
+	    [multi_line \
+		 "\\\* 1.1 ${not_nl} \\\(running\\\)${not_nl}" \
+		 "  2.1 ${not_nl} \\\(running\\\)"]
+    } elseif {$schedule_multiple == "on" && $follow_fork == "child"} {
+	# Both parent and child should be marked running, and the
+	# child should be selected.
+	gdb_test "info threads" \
+	    [multi_line \
+		 "  1.1 ${not_nl} \\\(running\\\)${not_nl}" \
+		 "\\\* 2.1 ${not_nl} \\\(running\\\)"]
+    } else {
+	set test "only $follow_fork marked running"
+	gdb_test_multiple "info threads" $test {
+	    -re "\\\(running\\\)${not_nl}\\\(running\\\)\r\n$gdb_prompt $" {
+		fail $test
+	    }
+	    -re "\\\* 1.1 ${not_nl}\\\(running\\\)\r\n  2.1 ${not_nl}\r\n$gdb_prompt $" {
+		gdb_assert [string eq $follow_fork "parent"] $test
+	    }
+	    -re "1.1 ${not_nl}\r\n\\\* 2.1 ${not_nl}\\\(running\\\)\r\n$gdb_prompt $" {
+		gdb_assert [string eq $follow_fork "child"] $test
+	    }
+	}
+    }
+
+    # We don't want to see "Inferior exited" in reaction to the kills.
+    gdb_test_no_output "set print inferior-events off"
+
+    # Kill both parent and child.
+    if {$detach_on_fork == "off" || $follow_fork == "parent"} {
+	gdb_test_no_output "kill inferior 1" "kill parent"
+    }
+    if {$detach_on_fork == "off" || $follow_fork == "child"} {
+	gdb_test_no_output "kill inferior 2" "kill child"
+    }
+}
+
+# Exercise all permutations of:
+#
+#  set detach-on-fork off|on
+#  set follow-fork parent|child
+#  set non-stop on|off
+#  set schedule-multiple on|off
+
+foreach_with_prefix detach-on-fork {"off" "on"} {
+    foreach_with_prefix follow-fork {"parent" "child"} {
+	with_test_prefix "non-stop" {
+	    do_test ${detach-on-fork} ${follow-fork} "on" "-"
+	}
+	with_test_prefix "all-stop" {
+	    foreach_with_prefix schedule-multiple {"on" "off"} {
+		do_test ${detach-on-fork} ${follow-fork} "off" ${schedule-multiple}
+	    }
+	}
+    }
+}
-- 
1.9.3