linux-kernel - Re: PID_NS unshare VS synchronize_rcu_tasks() (was: Re: [Syzkaller & bisect] There is task hung in "synchronize

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Message-ID: <20221123220648.GA1395324@lothringen>
Date:   Wed, 23 Nov 2022 23:06:48 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Pengfei Xu <pengfei.xu@...el.com>
Cc:     Lai Jiangshan <jiangshanlai@...il.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Christian Brauner <brauner@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, heng.su@...el.com,
        rcu@...r.kernel.org
Subject: Re: PID_NS unshare VS synchronize_rcu_tasks() (was: Re: [Syzkaller &
 bisect] There is task hung in "synchronize_rcu" in v6.1-rc5 kernel)

On Wed, Nov 23, 2022 at 11:45:50PM +0800, Pengfei Xu wrote:
> On 2022-11-23 at 15:37:58 +0100, Frederic Weisbecker wrote:
> > I have no idea how to solve the situation without violating the pid_namespace
> > rules and unshare() semantics (although I wish unshare(CLONE_NEWPID) had a less
> > error prone behaviour with allowing creating more than one task belonging to the
> > same namespace).
> > 
> > So probably having an SRCU read side critical section within exit_notify() is
> > not a good idea, is there a solution to work around that for rcu tasks?
> > 
>   Thanks for the analysis!
>   Add one more information: I tried to revert this commit only on top of
>   v6.1-rc5 mainline by script, but it caused kernel make to fail, it could not
>   confirm the bisect information is 100% accurate if I could not pass the
>   revert step verification. I just provide all the information I could.

No problem, I managed to reproduce with latest upstream.
I don't think the bisected commit is the culprit though, it may perhaps just make
the issue more likely to happen.

Thanks.

> 
>   And this issue is too difficult to me.
>   If I find more clue, I will update the eamil.
> 
>   Thanks!
>   BR.
> 
> > Thanks.