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    SubjectRe: [RFC] Proposal for ptrace improvements
    On Wed, Mar 2, 2011 at 12:32 PM, Indan Zupancic <indan@nul.nu> wrote:
    > On Wed, March 2, 2011 08:44, Tejun Heo wrote:
    >> On Wed, Mar 02, 2011 at 06:07:35AM +0100, Indan Zupancic wrote:
    >>> I'm not sure what Denys is talking about: Currently it's impossible to
    >>> pass along SIGSTOP to traced processes. Quoting the ptrace manpage:
    >>>
    >>>    PTRACE_CONT
    >>>           Restarts  the stopped child process.  If data is nonzero and not
    >>>           SIGSTOP, it is interpreted as a signal to be  delivered  to  the
    >>>           child;  otherwise,  no  signal is delivered.
    >>
    >> AFAICS, that's not true.  SIGSTOP isn't treated differently from other
    >> signals in the ptrace signal delivery path.  Maybe it was true in the
    >> past.
    >
    > Well, I can't find it in the code either, but it's probably a side-effect
    > of how ptrace is currently implemented. Test program code below, see for
    > yourself. I hope it's a program bug, but perhaps it's a kernel bug, as I
    > seem to get two SIGSTOP events when I allow the SIGSTOP, but only one when
    > denying it.

    This was discussed recently (again). Second SIGSTOP you see
    is a job control stop notification (as opposed to signal delivery notification).
    It's not a bug.

    --
    vda
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