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;
From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>
Cc:     Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: [PATCH printk v2 25/38] proc: consoles: document console_lock usage
Date:   Wed, 19 Oct 2022 17:01:47 +0206
Message-Id: <20221019145600.1282823-26-john.ogness@linutronix.de>
In-Reply-To: <20221019145600.1282823-1-john.ogness@linutronix.de>
References: <20221019145600.1282823-1-john.ogness@linutronix.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The console_lock is held throughout the start/show/stop procedure
to print out device/driver information about all registered
consoles. Since the console_lock is being used for multiple reasons,
explicitly document these reasons. This will be useful when the
console_lock is split into fine-grained locking.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 fs/proc/consoles.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
index cf2e0788f9c7..32512b477605 100644
--- a/fs/proc/consoles.c
+++ b/fs/proc/consoles.c
@@ -63,6 +63,14 @@ static void *c_start(struct seq_file *m, loff_t *pos)
 	struct console *con;
 	loff_t off = 0;
 
+	/*
+	 * Stop console printing because the device() callback may
+	 * assume the console is not within its write() callback.
+	 *
+	 * Hold the console_lock to guarantee safe traversal of the
+	 * console list. SRCU cannot be used because there is no
+	 * place to store the SRCU cookie.
+	 */
 	console_lock();
 	for_each_console(con)
 		if (off++ == *pos)
-- 
2.30.2