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    SubjectRe: [PATCH 11/11] ptrace: implement group stop notification for ptracer
    Date
    On Sunday 08 May 2011 17:49, Tejun Heo wrote:
    > Currently there's no way for ptracer to find out whether group stop
    > that tracee was in finished other than polling with PTRACE_GETSIGINFO.
    > Also, tracer can't detect new group stop started by an untraced thread
    > if tracee is already trapped. This patch implements group stop
    > notification for ptracer using INTERRUPT traps.
    >
    > When group stop state of a seized tracee changes, JOBCTL_TRAP_NOTIFY
    > is set, which triggers INTERRUPT trap but is sticky until the next
    > PTRACE_GETSIGINFO. As GETSIGINFO exports the current group stop
    > state, this guarantees that tracer checks the current group stop state
    > at least once after group stop state change. Stickiness is necessary
    > because notification trap may race with PTRACE_CONT for other traps
    > and get lost.

    To clarify on "sticky":

    Does this mean that if tracer userspace won't query PTRACE_GETSIGINFO,
    but will simply do:

    waitid(P_PID, tracee, NULL, WSTOPPED);
    ptrace(PTRACE_CONT, tracee, NULL, NULL);

    then kernel will generate INTERRUPT trap again and again
    (without letting tracee run) if job stop state of the tracee has changed?


    --
    vda


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