[PATCH printk v2 22/38] serial: kgdboc: document console_lock usage

John Ogness
2022-10-19T15:06:06Z

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>
---
drivers/tty/serial/kgdboc.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index e9d3f8c6e3dc..48000666789a 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -545,6 +545,14 @@ 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.
+ */
console_lock();
for_each_console(con) {
if (con->write && con->read &&
--
2.30.2