linux-kernel - Re: [PATCH 0/3] rcu-tasks: Fix race against exiting pid

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Date:   Mon, 28 Nov 2022 16:22:40 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Oleg Nesterov <oleg@...hat.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 0/3] rcu-tasks: Fix race against exiting pid_ns

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!!!

							Thanx, Paul

> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (3):
>       rcu-tasks: Improve comments explaining tasks_rcu_exit_srcu purpose
>       rcu-tasks: Remove preemption disablement around srcu_read_[un]lock() calls
>       rcu-tasks: Fix synchronize_rcu_tasks() VS zap_pid_ns_processes()
> 
> 
>  include/linux/rcupdate.h |  2 ++
>  kernel/pid_namespace.c   | 17 +++++++++++++++
>  kernel/rcu/tasks.h       | 55 ++++++++++++++++++++++++++++++++++++------------
>  3 files changed, 60 insertions(+), 14 deletions(-)