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    SubjectRe: [PATCH 3/3] rcu-tasks: Fix synchronize_rcu_tasks() VS zap_pid_ns_processes()
    On Tue, Dec 06, 2022 at 05:49:28PM +0100, Oleg Nesterov wrote:
    > 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.

    Given that this is not the first time that Tasks Trace RCU has been
    involved in a deadlock involving this exit path, I could certainly get
    behind this approach. ;-)

    Thanx, Paul

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