| Date | Wed, 27 Apr 2022 16:10:25 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held |
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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?
Oleg.
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