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    SubjectRe: [PATCH] ptrace: use safer wake up on ptrace_detach()
    On Tue, 1 Feb 2011 11:26:18 +0100
    Tejun Heo <tj@kernel.org> wrote:

    > The wake_up_process() call in ptrace_detach() is spurious and not
    > interlocked with the tracee state. IOW, the tracee could be running
    > or sleeping in any place in the kernel by the time wake_up_process()
    > is called. This can lead to the tracee waking up unexpectedly which
    > can be dangerous.
    >
    > The wake_up is spurious and should be removed but for now reduce its
    > toxicity by only waking up if the tracee is in TRACED or STOPPED
    > state.
    >
    > Signed-off-by: Tejun Heo <tj@kernel.org>
    > Cc: Roland McGrath <roland@redhat.com>
    > Cc: Oleg Nesterov <oleg@redhat.com>
    > Cc: stable@kernel.org

    Am unable to work out why you tagged it for backporting. It fixes some
    observed bug? Perhaps a regression?

    > Index: work/kernel/ptrace.c
    > ===================================================================
    > --- work.orig/kernel/ptrace.c
    > +++ work/kernel/ptrace.c
    > @@ -313,7 +313,7 @@ int ptrace_detach(struct task_struct *ch
    > child->exit_code = data;
    > dead = __ptrace_detach(current, child);
    > if (!child->exit_state)
    > - wake_up_process(child);
    > + wake_up_state(child, TASK_TRACED | TASK_STOPPED);
    > }
    > write_unlock_irq(&tasklist_lock);
    >


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