diff mbox series

[printk,v3,12/40] tty: serial: kgdboc: document console_lock usage

Message ID 20221107141638.3790965-13-john.ogness@linutronix.de
State New
Headers
Series reduce console_lock scope |

Commit Message

John Ogness Nov. 7, 2022, 2:16 p.m. UTC 
  kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
are unregistered until the kgdboc_earlycon is setup. This is necessary
because the trapping of the exit() callback assumes that the exit()
callback is not called before the trap is setup.

Explicitly document this non-typical console_lock usage.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---
 drivers/tty/serial/kgdboc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Daniel Thompson Nov. 9, 2022, 8:23 a.m. UTC | #1 
On Mon, Nov 07, 2022 at 03:22:10PM +0106, John Ogness wrote:
> kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
> are unregistered until the kgdboc_earlycon is setup. This is necessary
> because the trapping of the exit() callback assumes that the exit()
> callback is not called before the trap is setup.
>
> Explicitly document this non-typical console_lock usage.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>


Daniel.
Petr Mladek Nov. 9, 2022, 3:19 p.m. UTC | #2 
On Mon 2022-11-07 15:22:10, John Ogness wrote:
> kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
> are unregistered until the kgdboc_earlycon is setup. This is necessary
> because the trapping of the exit() callback assumes that the exit()
> callback is not called before the trap is setup.
> 
> Explicitly document this non-typical console_lock usage.

It is great to have the description.

> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Petr Mladek <pmladek@suse.com>

Best Regards,
Petr
diff mbox series

Patch

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index e76f0186c335..5be381003e58 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -530,6 +530,14 @@  static int __init kgdboc_earlycon_init(char *opt)
 	 * Look for a matching console, or if the name was left blank just
 	 * pick the first one we find.
 	 */
+
+	/*
+	 * Hold the console_lock to guarantee that no consoles are
+	 * unregistered until the kgdboc_earlycon setup is complete.
+	 * Trapping the exit() callback relies on exit() not being
+	 * called until the trap is setup. This also allows safe
+	 * traversal of the console list and race-free reading of @flags.
+	 */
 	console_lock();
 	for_each_console(con) {
 		if (con->write && con->read &&