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    SubjectRe: [PATCH 5/5] ptrace: implement PTRACE_LISTEN
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    On Tue, 2011-06-14 at 11:20 +0200, Tejun Heo wrote:

    [...]

    > + case PTRACE_LISTEN:
    > + /*
    > + * Listen for events. Tracee must be in STOP. It's not
    > + * resumed per-se but is not considered to be in TRACED by
    > + * wait(2) or ptrace(2). If an async event (e.g. group
    > + * stop state change) happens, tracee will enter STOP trap
    > + * again. Alternatively, ptracer can issue INTERRUPT to
    > + * finish listening and re-trap tracee into STOP.
    > + */
    > + if (unlikely(!seized || !lock_task_sighand(child, &flags)))
    > + break;
    > +
    > + si = child->last_siginfo;
    > + if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP))
    > + break;

    I've only just noticed this. You really don't want to break out of the
    switch while holding sighand->siglock. This should read,

    if (unlikely(!si || si->si_code >> 8 != PTRACE_EVENT_STOP)) {
    unlock_task_sighand(child, &flags);
    break;
    }

    --
    Matt Fleming, Intel Open Source Technology Center



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