linux-kernel - Re: locking API: was: [PATCH printk v1 00/18] serial: 8250: implement non-BKL console

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Message-ID: <ZCPw1pEakE7SGsKg@alley>
Date:   Wed, 29 Mar 2023 10:03:34 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Aaron Tomlin <atomlin@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        David Gow <davidgow@...gle.com>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        tangmeng <tangmeng@...ontech.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>, rcu@...r.kernel.org
Subject: Re: locking API: was: [PATCH printk v1 00/18] serial: 8250:
 implement non-BKL console

On Tue 2023-03-28 23:53:16, John Ogness wrote:
> On 2023-03-28, Petr Mladek <pmladek@...e.com> wrote:
> >> If an atomic context loses ownership while doing certain activities,
> >> it may need to re-acquire ownership in order to finish or cleanup
> >> what it started.
> >
> > This sounds suspicious. If a console/writer context has lost the lock
> > then all shared/locked resources might already be used by the new
> > owner.
> 
> Correct.
> 
> > I would expect that the context could touch only non-shared resources
> > after loosing the lock.
> 
> Correct.
> 
> The 8250 driver must disable interrupts before writing to the TX
> FIFO. After writing it re-enables the interrupts. However, it might be
> the case that the interrupts were already disabled, in which case after
> writing they are left disabled.

I see. The reacquire() makes sense now.

Thanks a lot for explanation.

Best Regards,
Petr