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    SubjectRe: [PATCH v2] Make PTRACE_SEIZE set ptrace options specified in 'data' parameter

    On Thu, Sep 08, 2011 at 08:17:47PM +0200, Oleg Nesterov wrote:
    > > There are places which assume ->ptrace is protected by siglock.
    > Really? Once again, I agree. But _afaics_ currently this is not strictly
    > needed. PT_PTRACED/PT_SEIZED should not go away under ->siglock, yes, but
    > it seems that it is fine to set them.

    Hmmm.... I haven't checked each direction. Maybe we don't strictly
    need it on setting it but I definitely was assuming that ->ptrace was
    protected by siglock while coding recent ptrace changes. Can't the
    following happen?

    * ptracer seizes child, sets PT_PTRACED and then OR PT_SEIZED.

    * ptracee enters signal delivery path with group stop scheduled.
    PT_PTRACED is visible and group stop is transformed into

    * ptracee enters do_jobct_trap(). PT_SEIZED is still not visible and
    it takes the path for the old behavior.

    * ptracer SEIZE'd and expects PTRACE_EVENT_STOP but it gets the old
    no-siginfo trap.

    > > and linking are protected by siglock
    > Hmm. Could you explain this? Why do want __ptrace_link under ->siglock ?

    Because it's much simpler to assume that w/ siglock locked, everything
    including ->parent is set up properly w.r.t. ->ptrace.



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