RE: [Patch] Broken multi-process detach

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

> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com] 
> Sent: Monday, July 16, 2012 1:24 PM
> To: Marc Khouzam
> Cc: 'gdb-patches@sourceware.org'
> Subject: Re: [Patch] Broken multi-process detach
> 
> On 07/16/2012 02:54 PM, Marc Khouzam wrote:
> > 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.
> 
> I'm not thinking of any.  Looks like I added it in the first
> async mode version of linux-nat.c (which was much rewritten
> later on).  Let's remove it.
> 
> Remove also the target_async call below:
> 
>   if (forks_exist_p ())
>     {
>       /* Multi-fork case.  The current inferior_ptid is being detached
> 	 from, but there are other viable forks to debug.  Detach from
> 	 the current fork, and context-switch to the first
> 	 available.  */
>       linux_fork_detach (args, from_tty);
> 
>       if (non_stop && target_can_async_p ())
>  	target_async (inferior_event_handler, 0);
> 
> 
> as this was re-installing the target on the event loop if there were
> other checkpoints (checkpoint/info checkpoint) to debug.  It is now
> unnecessary if we don't unregister from the event loop in the 
> first place.
> 
> > 
> > The testsuite hangs on HEAD so I wasn't able to run it yet.
> > But I'll do so once it works again.
> 
> It doesn't hang for me.  I've tested the patch on x86_64 
> Fedora 17, both
> sync and async modes.  No regressions.

Thanks for the help!

I checked-in the following:

2012-07-16  Marc Khouzam  <marc.khouzam@ericsson.com>
	    Pedro Alves  <palves@redhat.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 19:04:03 -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.  */
@@ -1892,9 +1892,6 @@
         the current fork, and context-switch to the first
         available.  */
       linux_fork_detach (args, from_tty);
-
-      if (non_stop && target_can_async_p ())
-       target_async (inferior_event_handler, 0);
     }
   else
     linux_ops->to_detach (ops, args, from_tty);