[PATCH printk v2 21/38] serial: kgdboc: use srcu console list iterator

John Ogness
2022-10-19T15:06:57Z

Use srcu console list iteration for safe console list traversal.

Note that configure_kgdboc() still requires the console_lock in
order to ensure that no console is in its write() callback when
its direct() callback is called. Add comments to clarify this.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
drivers/tty/serial/kgdboc.c | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index b17aa7e49894..e9d3f8c6e3dc 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -171,6 +171,7 @@ static int configure_kgdboc(void)
int err = -ENODEV;
char *cptr = config;
struct console *cons;
+ int cookie;

if (!strlen(config) || isspace(config[0])) {
err = 0;
@@ -193,8 +194,14 @@ static int configure_kgdboc(void)
if (!p)
goto noconfig;

+ /*
+ * Stop console printing because the device() callback may
+ * assume the console is not within its write() callback.
+ */
console_lock();
- for_each_console(cons) {
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(cons) {
int idx;
if (cons->device && cons->device(cons, &idx) == p &&
idx == tty_line) {
@@ -202,6 +209,8 @@ static int configure_kgdboc(void)
break;
}
}
+ console_srcu_read_unlock(cookie);
+
console_unlock();

kgdb_tty_driver = p;
@@ -451,6 +460,7 @@ static void kgdboc_earlycon_pre_exp_handler(void)
{
struct console *con;
static bool already_warned;
+ int cookie;

if (already_warned)
return;
@@ -463,9 +473,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
* serial drivers might be OK with this, print a warning once per
* boot if we detect this case.
*/
- for_each_console(con)
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(con) {
if (con == kgdboc_earlycon_io_ops.cons)
- return;
+ break;
+ }
+ console_srcu_read_unlock(cookie);
+ if (con)
+ return;

already_warned = true;
pr_warn("kgdboc_earlycon is still using bootconsole\n");
--
2.30.2