Oleg Nesterov <o...@redhat.com> writes: > On 04/26, Eric W. Biederman wrote: >> >> @@ -2164,7 +2166,9 @@ static void do_notify_parent_cldstop(struct >> task_struct *tsk, >> } >> >> sighand = parent->sighand; >> - spin_lock_irqsave(&sighand->siglock, flags); >> + lock = tsk->sighand != sighand; >> + if (lock) >> + spin_lock_nested(&sighand->siglock, SINGLE_DEPTH_NESTING); > > But why is it safe? > > Suppose we have two tasks, they both trace each other, both call > ptrace_stop() at the same time. Of course this is ugly, they both > will block. > > But with this patch in this case we have the trivial ABBA deadlock, > no?
I was thinking in terms of the process tree (which is fine). The ptrace parental relationship definitely has the potential to be a graph with cycles. Which as you point out is not fine. The result is very nice and I don't want to give it up. I suspect something ptrace cycles are always a problem and can simply be forbidden. That is going to take some analsysis and some additional code in ptrace_attach. I will go look at that. Eric _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
