linux-kernel - Re: [PATCH 1/7] General notification queue with user mmap()'able ring buffer

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Date:   Thu, 30 May 2019 11:50:39 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     David Howells <dhowells@...hat.com>, viro@...iv.linux.org.uk,
        raven@...maw.net, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org, linux-block@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/7] General notification queue with user mmap()'able
 ring buffer

> > Looking at the perf ring buffer, there appears to be a missing barrier in
> > perf_aux_output_end():
> > 
> > 	rb->user_page->aux_head = rb->aux_head;
> > 
> > should be:
> > 
> > 	smp_store_release(&rb->user_page->aux_head, rb->aux_head);
> > 
> > It should also be using smp_load_acquire().  See
> > Documentation/core-api/circular-buffers.rst
> > 
> > And a (partial) patch has been proposed: https://lkml.org/lkml/2018/5/10/249
> 
> So, if that's all that needs to be fixed, can you use the same
> buffer/code if that patch is merged?

That's about one year old...: let me add the usual suspects in Cc:  ;-)
since I'm not sure what the plan was (or if I'm missing something) ...

Speaking of ring buffer implementations (and relatively "old" patches),
here's another quite interesting:

  https://lkml.kernel.org/r/20181211034032.32338-1-yuleixzhang@tencent.com

Thanks,
  Andrea