Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 18 Jul 2023 12:18:47 +0900
From:   Sergey Senozhatsky <senozhatsky@chromium.org>
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk v3 4/7] printk: Do not take console lock for
 console_flush_on_panic()
Message-ID: <20230718031847.GB955071@google.com>
References: <20230717194607.145135-1-john.ogness@linutronix.de>
 <20230717194607.145135-5-john.ogness@linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230717194607.145135-5-john.ogness@linutronix.de>
Precedence: bulk

On (23/07/17 21:52), John Ogness wrote:
> 
> Currently console_flush_on_panic() will attempt to acquire the
> console lock when flushing the buffer on panic. If it fails to
> acquire the lock, it continues anyway because this is the last
> chance to get any pending records printed.
> 
> The reason why the console lock was attempted at all was to
> prevent any other CPUs from acquiring the console lock for
> printing while the panic CPU was printing. But as of the
> previous commit, non-panic CPUs will no longer attempt to
> acquire the console lock in a panic situation. Therefore it is
> no longer strictly necessary for a panic CPU to acquire the
> console lock.
> 
> Avoiding taking the console lock when flushing in panic has
> the additional benefit of avoiding possible deadlocks due to
> semaphore usage in NMI context (semaphores are not NMI-safe)
> and avoiding possible deadlocks if another CPU accesses the
> semaphore and is stopped while holding one of the semaphore's
> internal spinlocks.
> 
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>