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Date:   Wed, 10 Mar 2021 18:32:37 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Eric W. Biederman" <ebiederm@xmission.com>
Cc:     qianli zhao <zhaoqianligood@gmail.com>, christian@brauner.io,
        axboe@kernel.dk, Thomas Gleixner <tglx@linutronix.de>,
        Peter Collingbourne <pcc@google.com>,
        linux-kernel@vger.kernel.org, Qianli Zhao <zhaoqianli@xiaomi.com>
Subject: Re: [PATCH] exit: trigger panic when init process is set to
 SIGNAL_GROUP_EXIT
Message-ID: <20210310173236.GB8973@redhat.com>
References: <1615296712-175334-1-git-send-email-zhaoqianligood@gmail.com>
 <20210309182657.GA1408@redhat.com>
 <CAPx_LQEQto2fget=kCnfjSCdAp9XCwc2AWgzwxpbxdyCgNs5Mg@mail.gmail.com>
 <m1lfavufep.fsf@fess.ebiederm.org>
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On 03/10, Eric W. Biederman wrote:
>
> 	/* If global init has exited,
>          * panic immediately to get a useable coredump.
>          */
> 	if (unlikely(is_global_init(tsk) &&
> 	    (thread_group_empty(tsk) ||
>             (tsk->signal->flags & SIGNAL_GROUP_EXIT)))) {
> 		panic("Attempted to kill init!	exitcode=0x%08x\n",
>                 	tsk->signal->group_exit_code ?: (int)code);
> 	}
>
> The thread_group_empty test is needed to handle single threaded
> inits.

But we can't rely on thread_group_empty(). Just suppose that the main
thread exit first, then the 2nd (last) thread exits too.

Oleg.