PR remote/19496, timeout in forking-threads-plus-bkpt

This patch addresses a failure in
gdb.threads/forking-threads-plus-breakpoint.exp:

FAIL: gdb.threads/forking-threads-plus-breakpoint.exp: cond_bp_target=1:
detach_on_fork=on: inferior 1 exited (timeout)

Cause:

A fork event was reported to GDB before GDB knew about the parent
thread, followed immediately by a breakpoint event in a different
thread.  The parent thread was subsequently added via
remote_notice_new_inferior in process_stop_reply, but when the thread
was added the thread_info.state was set to THREAD_STOPPED.  The fork
event was then handled correctly, but when the fork parent was resumed
via a call to keep_going, the state was unchanged.

The breakpoint event was then handled, which caused all the
non-breakpoint threads to be stopped.  When the breakpoint thread was
resumed, all the non-breakpoint threads were resumed via
infrun.c:restart_threads.  Our old fork parent wasn't restarted,
because it still had thread_info.state set to THREAD_STOPPED.
Ultimately the program under debug hung waiting for a pthread_join
while the old fork parent was stopped forever by GDB.

Fix:

Since this is non-stop, then the bug is that the thread should have
been added in THREAD_RUNNING state.  Consider that infrun may be
pulling target events out of the target_ops backend into its own event
queue, but, not process them immediately.  E.g., infrun may be
stopping all threads temporarily for a step-over-breakpoint operation
for thread A (stop_all_threads).  The waitstatus of all threads is
thus left pending in the thread structure (save_status), including the
fork event of thread B.  Right at this point, if the user does "info
threads", that should show thread B (the fork parent) running, not
stopped, even if internally, gdb is holding it paused for a little
bit.

Thus if in non-stop mode, always add new threads in the external
user-visible THREAD_RUNNING state.  Change remote_notice_new_inferior
to accept the internal executing state of the thread instead, with
EXECUTING set to 1 when we discover a thread that is running on the
target (such as through remote_update_thread_list), and 0 when the
thread is really paused (such as when we see a stop reply).

Tested on x86_64 Linux and Nios II Linux target with x86 Linux host.

gdb/ChangeLog:
2016-03-17  Pedro Alves  <palves@redhat.com>
	    Don Breazeal  <donb@codesourcery.com>

	PR remote/19496
	* infcmd.c (notice_new_inferior): Use the 'leave_running' argument
	instead of checking the 'non_stop' global.
	* remote.c (remote_add_thread): New parameter 'executing'.  Use it
	to set the new thread's executing state.
	(remote_notice_new_inferior): Rename parameter 'running' to
	'executing'.  Always set the thread state to THREAD_RUNNING in
	non-stop mode, and to THREAD_STOPPED in all-stop mode.  Pass
	EXECUTING to remote_add_thread and notice_new_inferior.
	(remote_update_thread_list): Update to pass executing state, not
	running state.

1 files changed, 1 insertions, 6 deletions

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index a80bf0a..d687116 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -2903,11 +2903,7 @@ notice_new_inferior (ptid_t ptid, int leave_running, int from_tty)
 
   old_chain = make_cleanup (null_cleanup, NULL);
 
-  /* If in non-stop, leave threads as running as they were.  If
-     they're stopped for some reason other than us telling it to, the
-     target reports a signal != GDB_SIGNAL_0.  We don't try to
-     resume threads with such a stop signal.  */
-  mode = non_stop ? ATTACH_POST_WAIT_RESUME : ATTACH_POST_WAIT_NOTHING;
+  mode = leave_running ? ATTACH_POST_WAIT_RESUME : ATTACH_POST_WAIT_NOTHING;
 
   if (!ptid_equal (inferior_ptid, null_ptid))
     make_cleanup_restore_current_thread ();
@@ -2943,7 +2939,6 @@ notice_new_inferior (ptid_t ptid, int leave_running, int from_tty)
       return;
     }
 
-  mode = leave_running ? ATTACH_POST_WAIT_RESUME : ATTACH_POST_WAIT_NOTHING;
   attach_post_wait ("" /* args */, from_tty, mode);
 
   do_cleanups (old_chain);