Re: [RFC PATCH] set TASK_TRACED before arch_ptrace code to fix a race

["Luming Yu" <luming.yu@gmail.com>]

On Fri, May 23, 2008 at 4:34 AM, Roland McGrath <roland@redhat.com> wrote:
>> Sorry for confusion, Let me try to explain it more:
>
> I understand these code paths (I wrote them).
>
>> If TASK_TRACED is not set earlier before arch_ptrace_stop on ia64
>> ptrace_notify code path, some signals would be delivered without
>> letting debugger run.. (i.e. PTRACED logica in get_signal_to_deliver
>> would be ignored totally!). These should cause the test case hang on
>> ia64. And x86 just works..
>
> I do not understand this at all, and it has given no information you did
> not give before.  Please describe the scenario you see in fine-grained
> terms.
>
In the code path mentioned above, I see only ia64 has chance to let
ptraced thread deliver those pending signals before TASK_TRACED is
set. Then debugger thread would lose chance to interfere the
delivering of those signals if I correctly understand PT_PTRACED logic
in get_signal_to_deliver, and the relationship between the two flag :
TASK_TRACED and PT_TRACED.

Since you write those code, Please clarify, in ptrace_notify code
path, is it allowed that ptraced thread can run signal handler without
telling debugger what happened?

I noticed the only difference between x86 and IA64 ,  and it does make
the test case work on
x86, and fail on IA64... So I made the patch trying to eliminate the
difference. It indeed seems to solve my problem although it is still
hack, and I don't know what kind of signals strace handled has such
magic..

As for how the door is only open for ia64, I can explain further if
you want to know.