linux-kernel - Re: Question on comment header for for_each

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Message-ID: <20181108092151.GM9761@hirez.programming.kicks-ass.net>
Date:   Thu, 8 Nov 2018 10:21:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: Question on comment header for for_each_domain()

On Wed, Nov 07, 2018 at 03:00:02PM -0800, Paul E. McKenney wrote:
> Hello!
> 
> The header comment for for_each_domain() talks about a call to
> synchronize_sched() within detach_destroy_domains(), but I am not
> seeing any such call.  Because synchronize_sched() is now folded into
> synchronize_rcu(), I have a patch that edits the comment, but it looks
> like a larger change is needed.
> 
> Or am I blind today?

I think you're quite right and that comment is a wee bit stale.

The sched domain tree is indeed protected by regular RCU (not RCU-sched
as the comment seems to imply) and this is per destroy_sched_domains()
using call_rcu().

And most (I didn't look at all) uses for the sched-domain tree do indeed
employ rcu_read_lock().