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Date:   Wed, 29 Mar 2023 10:03:34 +0200
From:   Petr Mladek <pmladek@suse.com>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Jason Wessel <jason.wessel@windriver.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Douglas Anderson <dianders@chromium.org>,
        Aaron Tomlin <atomlin@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        kgdb-bugreport@lists.sourceforge.net,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-fsdevel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        "Guilherme G. Piccoli" <gpiccoli@igalia.com>,
        David Gow <davidgow@google.com>,
        Tiezhu Yang <yangtiezhu@loongson.cn>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        tangmeng <tangmeng@uniontech.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>, rcu@vger.kernel.org
Subject: Re: locking API: was: [PATCH printk v1 00/18] serial: 8250:
 implement non-BKL console
Message-ID: <ZCPw1pEakE7SGsKg@alley>
References: <20230302195618.156940-1-john.ogness@linutronix.de>
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On Tue 2023-03-28 23:53:16, John Ogness wrote:
> On 2023-03-28, Petr Mladek <pmladek@suse.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