[PATCH printk v2 28/38] printk: console_unblank: use srcu console list iterator

John Ogness
2022-10-19T15:05:58Z

Use srcu console list iteration for console list traversal.

Document why the console_lock is still necessary.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index c4d5d58b5977..0c37ab208395 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2948,10 +2948,14 @@ EXPORT_SYMBOL(console_conditional_schedule);
void console_unblank(void)
{
struct console *c;
+ int cookie;

/*
- * console_unblank can no longer be called in interrupt context unless
- * oops_in_progress is set to 1..
+ * Stop console printing because the unblank() callback may
+ * assume the console is not within its write() callback.
+ *
+ * If @oops_in_progress is set, this may be an atomic context.
+ * In that case, attempt a trylock as best-effort.
*/
if (oops_in_progress) {
if (down_trylock_console_sem() != 0)
@@ -2961,9 +2965,14 @@ void console_unblank(void)

console_locked = 1;
console_may_schedule = 0;
- for_each_console(c)
+
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
if (console_is_enabled(c) && c->unblank)
c->unblank();
+ }
+ console_srcu_read_unlock(cookie);
+
console_unlock();

if (!oops_in_progress)
--
2.30.2