Re: [gdbserver] Problems trying to resume dead threads

[Daniel Jacobowitz <drow@false.org>]

Sorry - as you can see, I am once again behind on gdb-patches.

On Sat, Jul 19, 2008 at 07:16:48PM +0200, Ulrich Weigand wrote:
> Hello,
> 
> gdbserver on Linux seems to have difficulties handling
> the case where a thread dies while it is stopped.  This can
> happen during the loop over all threads in linux_resume:

I can reproduce this problem by using the binary from killed.exp and
running strace on gdbserver.  I can also reproduce it on an embedded
ARM target by running killed.exp.  I can't reproduce it on my desktop
running killed.exp, which suggests this is normally hidden by
scheduler decisions - you need a long enough gap between the two
PTRACE_CONT's.

What do you think of this change?  Ideally, we could wait with WNOHANG
at this point to check for the exit case, but we'd have to restructure
a bit of the event loop to handle pending status == exited.

-- 
Daniel Jacobowitz
CodeSourcery

2008-08-04  Daniel Jacobowitz  <dan@codesourcery.com>

	* linux-low.c (linux_resume_one_process): Ignore ESRCH.

Index: linux-low.c
===================================================================
RCS file: /cvs/src/src/gdb/gdbserver/linux-low.c,v
retrieving revision 1.79
diff -u -p -r1.79 linux-low.c
--- linux-low.c	28 Jul 2008 18:28:56 -0000	1.79
+++ linux-low.c	4 Aug 2008 13:38:24 -0000
@@ -1193,7 +1193,19 @@ linux_resume_one_process (struct inferio
 
   current_inferior = saved_inferior;
   if (errno)
-    perror_with_name ("ptrace");
+    {
+      /* ESRCH from ptrace either means that the thread was already
+	 running (an error) or that it is gone (a race condition).  If
+	 it's gone, we will get a notification the next time we wait,
+	 so we can ignore the error.  We could differentiate these
+	 two, but it's tricky without waiting; the thread still exists
+	 as a zombie, so sending it signal 0 would succeed.  So just
+	 ignore ESRCH.  */
+      if (errno == ESRCH)
+	return;
+
+      perror_with_name ("ptrace");
+    }
 }
 
 static struct thread_resume *resume_ptr;