linux-kernel - Re: Mutual debugging of 2 processes can stuck in unkillable stopped state

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Message-ID: <20210413171741.GA7672@redhat.com>
Date:   Tue, 13 Apr 2021 19:17:43 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Igor Zhbanov <i.zhbanov@...russia.ru>
Cc:     linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Mutual debugging of 2 processes can stuck in unkillable stopped
 state

Hi Igor,

sorry for delay...

On 04/12, Igor Zhbanov wrote:
>
> Hi Oleg,
>
> So what is the cause of this problem?

The cause is clear. And well known ;) And again, this has almost nothing to do
with the mutual debugging.

The tracee sleeps in ptrace_stop(). You send SIGKILL. This wakes the tracee up,
it dequeues the signal, calls do_exit(), and stops again in PTRACE_EVENT_EXIT.
With SIGKILL in signal->shared_pending. This all looks as if the tracee doesn't
react to SIGKILL.

The only problem is that any change can break something which relies on the
current behaviour :/ I'll write another email on this.

Oleg.