[PATCH printk v2 23/38] tty: tty_io: document console_lock usage

John Ogness
2022-10-19T15:06:39Z

show_cons_active() uses the console_lock to gather information
on 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>
---
drivers/tty/tty_io.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 2050e63963bb..333579bfa335 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3526,6 +3526,14 @@ static ssize_t show_cons_active(struct device *dev,
struct console *c;
ssize_t count = 0;

+ /*
+ * Hold the console_lock to guarantee that no consoles are
+ * unregistered until all console processing is complete.
+ * This also allows safe traversal of the console list.
+ *
+ * Stop console printing because the device() callback may
+ * assume the console is not within its write() callback.
+ */
console_lock();
for_each_console(c) {
if (!c->device)
--
2.30.2