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Re: [gdbserver] Problems trying to resume dead threads
- From: Daniel Jacobowitz <drow at false dot org>
- To: Ulrich Weigand <uweigand at de dot ibm dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Mon, 4 Aug 2008 09:40:00 -0400
- Subject: Re: [gdbserver] Problems trying to resume dead threads
- References: <200807191716.m6JHGmsA013958@d12av02.megacenter.de.ibm.com>
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;