[PING]Re: [PATCH v2 3/3] PR remote/19496, timeout in forking-threads-plus-bkpt

[Don Breazeal <donb at codesourcery dot com>]

Ping
Thanks,
--Don

On 2/10/2016 4:28 PM, Don Breazeal wrote:
> On 2/1/2016 12:09 PM, Pedro Alves wrote:
>> On 02/01/2016 07:29 PM, Don Breazeal wrote:
>>> On 2/1/2016 4:05 AM, Pedro Alves wrote:
>>
>>> Hi Pedro,
> ---snip---
>>> 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.
>>
>> Since this is non-stop, then it sounds to me like 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.
>>
> 
> Hi Pedro,
> Here is a new patch that adds the threads with the state set to
> THREAD_RUNNING for fork events.
> Thanks!
> --Don
> 
> 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:
> Make sure to add the fork parent thread in the THREAD_RUNNING state by
> calling remote_notice_new_inferior with RUNNING set to 1 when processing
> a fork stop reply.
> 
> Tested on x86_64 Linux and Nios II Linux target with x86 Linux host.
> 
> gdb/ChangeLog:
> 2016-02-10  Don Breazeal  <donb@codesourcery.com>
> 
> 	* remote.c (process_stop_reply): Call remote_notice_new_inferior
> 	with RUNNING set to 1 when handling fork events.
> 
> ---
>  gdb/remote.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/remote.c b/gdb/remote.c
> index f09a06e..ab750a7 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -6818,7 +6818,14 @@ process_stop_reply (struct stop_reply *stop_reply,
>  	  VEC_free (cached_reg_t, stop_reply->regcache);
>  	}
>  
> -      remote_notice_new_inferior (ptid, 0);
> +      /* If a fork event arrived before we knew about the parent thread,
> +	 make sure to mark it as running when it is created.  */
> +      if (status->kind == TARGET_WAITKIND_FORKED
> +	  || status->kind == TARGET_WAITKIND_VFORKED)
> +	remote_notice_new_inferior (ptid, 1);
> +      else
> +	remote_notice_new_inferior (ptid, 0);
> +
>        remote_thr = demand_private_info (ptid);
>        remote_thr->core = stop_reply->core;
>        remote_thr->stop_reason = stop_reply->stop_reason;
>