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

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Message-ID: <c0131d23-fb09-7622-d51d-30e094d92136@omprussia.ru>
Date:   Mon, 29 Mar 2021 20:44:41 +0300
From:   Igor Zhbanov <i.zhbanov@...russia.ru>
To:     Oleg Nesterov <oleg@...hat.com>
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 Oleg,

On 29.03.2021 20:38, Oleg Nesterov wrote:
> Hi Igor,
> 
> So. As expected, they sleep in EVENT_EXIT _after_ you have already
> sent SIGKILL.

Here is the processes stack before sending any signals to them:

izh@...e2:~> sudo cat /proc/1751/stack
[<0>] ptrace_stop+0x14e/0x260
[<0>] ptrace_do_notify+0x91/0xb0
[<0>] ptrace_notify+0x4e/0x70
[<0>] syscall_slow_exit_work+0x90/0x150
[<0>] do_syscall_64+0x129/0x1f0
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

izh@...e2:~> sudo cat /proc/1979/stack
[<0>] ptrace_stop+0x14e/0x260
[<0>] get_signal+0x4d5/0x840
[<0>] do_signal+0x30/0x6a0
[<0>] exit_to_usermode_loop+0x8b/0x120
[<0>] do_syscall_64+0x1c3/0x1f0
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

> Igor, thanks for your report, but (I think) this has nothing to do
> with mutual debugging. I'll return to this problem in a couple of
> days, I'm a bit busy right now.

Sorry for inexact description. I said it from the user perspective when
the processes are stopped and can't be killed. :-)