Re: [PATCH stable-3.0] ptrace: don't clear GROUP_STOP_SIGMASK ondouble-stop

[Oleg Nesterov]

On 09/26, Oleg Nesterov wrote:
>
> 1. Luke Macken triggered WARN_ON(!(group_stop & GROUP_STOP_SIGMASK))
>    in do_signal_stop().
>
>    This is because do_signal_stop() clears GROUP_STOP_SIGMASK part
>    unconditionally but doesn't update it if task_is_stopped().
>
> 2. Looking at this problem I noticed that WARN_ON_ONCE(!ptrace) is
>    not right, a stopped-but-resumed tracee can clone the untraced
>    thread in the SIGNAL_STOP_STOPPED group, the new thread can start
>    another group-stop.
>
>    Remove this warning, we need more fixes to make it true.

Tejun, 3.1 has similar problems. I'll write another email...

Oleg.

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