linux-kernel - Re: [PATCH 3/4 UPDATED] scheduler: replace migration_thread with cpu

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Date:	Thu, 6 May 2010 11:42:52 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	mingo@...e.hu, peterz@...radead.org, linux-kernel@...r.kernel.org,
	Dipankar Sarma <dipankar@...ibm.com>,
	Josh Triplett <josh@...edesktop.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Dimitri Sivanich <sivanich@....com>
Subject: Re: [PATCH 3/4 UPDATED] scheduler: replace migration_thread with
 cpu_stop

On Thu, May 06, 2010 at 06:30:40PM +0200, Tejun Heo wrote:
> On 05/05/2010 10:31 PM, Paul E. McKenney wrote:
> > Almost.  With the following patch, I am good with it.
> 
> Ah, right.  What was I thinking?  I'll include your patch and push it
> to Ingo.  Thanks.

And of course, I overdid it in my patch when I removed smp_mb() from
the !SMP version of synchronize_sched_expedited().  :-/

If synchronize_sched_expedited() is ever to be invoked from within
kernel/sched.c in a UP kernel, there needs to be a "barrier()" in the
!SMP version.  So please see the following patch.

							Thanx, Paul

commit 0eab52c0eeeb8507a83bdb37cc8f690b1c4f4a2c
Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Date:   Thu May 6 11:40:17 2010 -0700

    rcu: need barrier() in UP synchronize_sched_expedited()
    
    If synchronize_sched_expedited() is ever to be called from within
    kernel/sched.c in a !SMP PREEMPT kernel, the !SMP implementation needs
    a barrier().
    
    Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/sched.c b/kernel/sched.c
index 155a16d..fbaf312 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8932,6 +8932,7 @@ struct cgroup_subsys cpuacct_subsys = {
 
 void synchronize_sched_expedited(void)
 {
+	barrier();
 }
 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
 
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