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

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Date: Mon, 29 Apr 2024 11:57:12 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	LKML <linux-kernel@...r.kernel.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 Mon, Apr 29, 2024 at 01:03:28PM +0200, Oleg Nesterov wrote:
> 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>

Queued, thank you both!

							Thanx, Paul