linux-kernel - Re: [PATCH 3/3] rcu-tasks: Fix synchronize_rcu_tasks() VS zap_pid_ns

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Message-ID: <20221206164927.GD3866@redhat.com>
Date:   Tue, 6 Dec 2022 17:49:28 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>, rcu@...r.kernel.org
Subject: Re: [PATCH 3/3] rcu-tasks: Fix synchronize_rcu_tasks() VS
 zap_pid_ns_processes()

On 11/30, Eric W. Biederman wrote:
>
> 2) I keep thinking zap_pid_ns_processes() should be changed so that
>    after it sends SIGKILL to all of the relevant processes to not wait,

At least I think it should not wait for the tasks injected into this ns.

Because this looks like a kernel bug even if we forget about this deadlock.

Say we create a task P using clone(CLONE_NEWPID), then inject a task T into
P's pid-namespace via setns/fork. This make the process P "unkillable", it
will hang in zap_pid_ns_processes() "forever" until T->parent reaps a zombie
task T killed by P.

Oleg.