linux-kernel - Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer implementation

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Date:   Fri, 21 Jun 2019 14:16:53 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v2 1/2] printk-rb: add a new printk ringbuffer
 implementation

> > FWIW (and as anticipated time ago in a private email), when I see code
> > like this I tend to look elsewhere...  ;-/
> 
> Do you really mean "code" or are you just referring to "code comments"?
> If you really mean code, then I'd appreciate some feedback about what
> should change.

I really just meant "uncommented code".  ;-)  I do plan to read your:

  https://lkml.kernel.org/r/87k1df28x4.fsf@linutronix.de

(and the code it's referring to) with due calm in the following days.
Thank you in advance for these remarks.

[Trying to address your question about herd7,]

A list of supported primitives is available from:

  tools/memory-model/linux-kernel.def	(left column)

This includes cmpxchg() (and its variants: _relaxed(), _acquire() and
_release()), however, herd7 can currently only parse statements like:

  loc_var = cmpxchg(addr, old, new);

(and it will complain loudly without that "loc_var = " part...); this
is something that could be improved, or at least it seems this way...

A similar consideration holds for all the value-returning primitives.

Thanks,
  Andrea