linux-kernel - Re: printk meeting at LPC

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Message-ID: <877e66nfdz.fsf@linutronix.de>
Date:   Wed, 18 Sep 2019 11:05:28 +0200
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Andrea Parri <parri.andrea@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Theodore Ts'o <tytso@....edu>, Paul Turner <pjt@...gle.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: printk meeting at LPC

On 2019-09-18, Sergey Senozhatsky <sergey.senozhatsky.work@...il.com> wrote:
>> Each console has its own iterator. This iterators will need to
>> advance, regardless if the message was printed via write() or
>> write_atomic().
>
> Great.
>
> ->atomic_write() path will make sure that kthread is parked or will
> those compete for uart port?

A cpu-lock (probably per-console) will be used to synchronize the
two. Unlike my RFCv1, we want to keep the cpu-lock out of the console
drivers and we want it to be less aggressive (using trylock's instead of
spinning). This should make the cpu-lock less "dangerous". I talked with
PeterZ, Thomas, and PetrM about how this can be implemented, but there
may still be some corner cases.

I would like to put everything together now so that we can run and test
if the decisions made in that meeting hold up for all the cases. I think
it will be easier to identify/add the missing pieces, once we have it
coded.

John Ogness