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Date:   Fri, 2 Dec 2022 23:55:34 +0100
From:   Frederic Weisbecker <frederic@kernel.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>, rcu@vger.kernel.org
Subject: Re: [PATCH 0/3] rcu-tasks: Fix race against exiting pid_ns
Message-ID: <20221202225534.GB1754872@lothringen>
References: <20221125135500.1653800-1-frederic@kernel.org>
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 <20221129095500.GA1706373@lothringen>
 <20221129144834.GW4001@paulmck-ThinkPad-P17-Gen-1>
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On Tue, Nov 29, 2022 at 06:48:34AM -0800, Paul E. McKenney wrote:
> On Tue, Nov 29, 2022 at 10:55:00AM +0100, Frederic Weisbecker wrote:
> > On Mon, Nov 28, 2022 at 04:22:40PM -0800, Paul E. McKenney wrote:
> > > On Fri, Nov 25, 2022 at 02:54:57PM +0100, Frederic Weisbecker wrote:
> > > > Pengfei Xu has reported a deadlock involving calls to unshare(),
> > > > perf_event_open() and clone3() calls. It requires CAP_SYS_ADMIN
> > > > to reproduce (at least I don't see a way for a non privilege process to
> > > > reproduce).
> > > > 
> > > > See this thread for details: https://lore.kernel.org/all/Y3sOgrOmMQqPMItu@xpf.sh.intel.com/
> > > > And this document for the collaborative analysis with Boqun, Paul and Neeraj:
> > > > https://docs.google.com/document/d/1hJxgiZ5TMZ4YJkdJPLAkRvq7sYQ-A7svgA8no6i-v8k
> > > > 
> > > > The two first patches are small improvements. The fix is in the last patch.
> > > > 
> > > > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> > > > 	rcu/dev
> > > > 
> > > > HEAD: 45ef5a0a4be4e0db9eadcc86e8f346d34c62e744
> > > 
> > > Hearing no objections, queued for further review and testing.
> > > 
> > > And thank you very much!  That race between synchronize_rcu_tasks() and
> > > zap_pid_ns_processes() certainly was more than a bit on the non-trivial
> > > side.  Good show!!!
> > 
> > Thanks!
> > 
> > Also please replace the last patch with the following to fix
> > a !CONFIG_RCU_TASKS issue:
> 
> Like this?  ;-)
> 
> a0c355bbdfee ("squash! rcu-tasks: Fix synchronize_rcu_tasks() VS zap_pid_ns_processes()")

You got it! :)