linux-kernel - Re: [PATCH 1/2] kthread: add barriers to set_kthread_struct() and to

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Message-ID: <20170316155534.zbtmy5v7gh6pbuhl@hirez.programming.kicks-ass.net>
Date:   Thu, 16 Mar 2017 16:55:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, Chris Mason <clm@...com>,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 1/2] kthread: add barriers to set_kthread_struct() and
 to_kthread()

On Thu, Mar 16, 2017 at 11:38:43AM -0400, Tejun Heo wrote:
> On Thu, Mar 16, 2017 at 11:33:01AM -0400, Tejun Heo wrote:
> > > And perhaps we should add another helper, say,
> > > 
> > > 	#define lockless_assign_pointer(ptr, val)	\
> > > 		smp_store_release(&ptr, val)
> > > 
> > > for set_kthread_struct() ? it can have more users.
> > > 
> > > Not that I think you should change your patch, I am just asking.
> > 
> > Ah yeah, that would look better.  I vaguely remembered the new macro
> > but couldn't quite remember it fully. :)  Will update the patch.
> 
> Oops, as for adding lockless_assign_pointer(), wouldn't smp_wmb() be a
> better match for smp_read_barrier_depends()?  ISTR acquire/release
> pairs being more expensive on some archs.

88c1863066cc ("rcu: Define rcu_assign_pointer() in terms of smp_store_release()")