On Thu, Nov 22, 2007 at 07:14:59PM +0300, Oleg Nesterov wrote:
> If the tracer went away (may_ptrace_stop() failed), ptrace_stop() drops tasklist
> and then changes the ->state from TASK_TRACED to TASK_RUNNING.
>
> This can fool another tracer which attaches to us in between. Change the ->state
> under tasklist_lock to ensure that ptrace_check_attach() can't wrongly succeed.
ptrace_check_attach? Both do read_lock -- can run in parallel, so how can it help?
> --- PT/kernel/signal.c~1_ptrace_stop 2007-11-21 21:41:02.000000000 +0300
> +++ PT/kernel/signal.c 2007-11-22 16:59:35.000000000 +0300
> @@ -1628,11 +1628,11 @@ static void ptrace_stop(int exit_code, i
> } else {
> /*
> * By the time we got the lock, our tracer went away.
> - * Don't stop here.
> + * Don't drop the lock yet, another tracer may come.
> */
> - read_unlock(&tasklist_lock);
> - set_current_state(TASK_RUNNING);
> + __set_current_state(TASK_RUNNING);
> current->exit_code = nostop_code;
> + read_unlock(&tasklist_lock);
> }
>
> /*
-
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