[Patch] Broken multi-process detach

[Marc Khouzam <marc dot khouzam at ericsson dot com>]

Hi,

Detaching from an inferior in multi-process is broken.
The problem seems to be that in linux_nat.c:linux_nat_detach()
GDB first unregisters from the event loop by calling 
linux_nat_async (NULL, 0).  In multi-process, further
events received from running inferiors are missed; breakpoint
hits are not reported, interrupting a thread is not reported,
and so on.  See below for a broken session example.

We could remove the call to linux_nat_async (NULL, 0) but I didn't
know if that would have bad side-effects.  Here is the patch that
does that, if it is felt that is the correct solution.

The testsuite hangs on HEAD so I wasn't able to run it yet.
But I'll do so once it works again.

Thanks

Marc

2012-07-16  Marc Khouzam  <marc.khouzam@ericsson.com>

        * linux_nat.c (linux_nat_detach): Don't unregister from the event
        loop.

### Eclipse Workspace Patch 1.0
#P src
Index: gdb/linux-nat.c
===================================================================
RCS file: /cvs/src/src/gdb/linux-nat.c,v
retrieving revision 1.254
diff -u -r1.254 linux-nat.c
--- gdb/linux-nat.c     7 Jul 2012 12:13:56 -0000       1.254
+++ gdb/linux-nat.c     16 Jul 2012 12:44:38 -0000
@@ -1848,8 +1848,8 @@
 
   pid = GET_PID (inferior_ptid);
 
-  if (target_can_async_p ())
-    linux_nat_async (NULL, 0);
+  /* Don't unregister from the event loop, as there may be other
+     inferiors running. */
 
   /* Stop all threads before detaching.  ptrace requires that the
      thread is stopped to sucessfully detach.  */


Broken session:
==============
> gdb.7.5
GNU gdb (GDB) 7.4.50.20120714-cvs

==> set non-stop and start two inferiors
[...]

(gdb) inf thread
  Id   Target Id         Frame 
  2    process 23634     (running)
* 1    process 23629     main () at loopfirst.noprint.cc:5
(gdb) detach
Detaching from program: /home/lmckhou/testing/loopfirst.noprint, process 23629
(gdb) inf thread
  Id   Target Id         Frame 
  2    process 23634     (running)

No selected thread.  See `help thread'.
(gdb) thread 2
[Switching to thread 2 (process 23634)](running)

=> interrupt the running thread

(gdb) interrupt
(gdb) inf thread
  Id   Target Id         Frame 
* 2    process 23634     (running)

=> event not received, thread still marked running

(gdb) c
Continuing.
Cannot execute this command while the selected thread is running.