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

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Date: Mon, 29 Apr 2024 13:03:28 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, rcu <rcu@...r.kernel.org>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH] Revert "rcu-tasks: Fix synchronize_rcu_tasks() VS
 zap_pid_ns_processes()"

On 04/25, Frederic Weisbecker wrote:
>
> This reverts commit 28319d6dc5e2ffefa452c2377dd0f71621b5bff0. The race
> it fixed was subject to conditions that don't exist anymore since:
>
> 	1612160b9127 ("rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks")
>
> This latter commit removes the use of SRCU that used to cover the
> RCU-tasks blind spot on exit between the tasklist's removal and the
> final preemption disabling. The task is now placed instead into a
> temporary list inside which voluntary sleeps are accounted as RCU-tasks
> quiescent states. This would disarm the deadlock initially reported
> against PID namespace exit.
>
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  include/linux/rcupdate.h |  2 --
>  kernel/pid_namespace.c   | 17 -----------------
>  kernel/rcu/tasks.h       | 16 +++-------------
>  3 files changed, 3 insertions(+), 32 deletions(-)

LGTM. FWIW,

Reviewed-by: Oleg Nesterov <oleg@...hat.com>