linux-kernel - Re: [PATCH 2/2] rcu/tasks: Further comment ordering around current task snapshot on TASK-TRACE

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Message-ID: <b3018a43-02af-47f9-b7e9-a639dfd026f5@paulmck-laptop>
Date: Tue, 21 May 2024 06:38:15 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: 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>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] rcu/tasks: Further comment ordering around current
 task snapshot on TASK-TRACE

On Tue, May 21, 2024 at 11:59:57AM +0200, Frederic Weisbecker wrote:
> Le Mon, May 20, 2024 at 04:25:33PM -0700, Paul E. McKenney a écrit :
> > Good points!  How about the following?
> > 
> > 		// Note that cpu_curr_snapshot() picks up the target
> > 		// CPU's current task while its runqueue is locked with
> > 		// an smp_mb__after_spinlock().  This ensures that either
> > 		// the grace-period kthread will see that task's read-side
> > 		// critical section or the task will see the updater's pre-GP
> > 		// accesses.  The trailng smp_mb() in cpu_curr_snapshot()
> 
> *trailing

Good catch!

> > 		// does not currently play a role other than simplify
> > 		// that function's ordering semantics.  If these simplified
> > 		// ordering semantics continue to be redundant, that smp_mb()
> > 		// might be removed.
> > 
> > Keeping in mind that the commit's log fully lays out the troublesome
> > scenario.
> 
> Yep, looks very good!
> 
> Thanks!

Very good, I will fold this in on my next rebase.

							Thanx, Paul