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

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Message-ID: <20170316153843.GB15810@htj.duckdns.org>
Date:   Thu, 16 Mar 2017 11:38:43 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.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 11:33:01AM -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.

Thanks.

-- 
tejun