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

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Date: Tue, 21 May 2024 11:59:57 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...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

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

> 		// 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!

> 
> 							Thanx, Paul
>