[PATCH printk v3 20/40] printk: __pr_flush: use srcu console list iterator

From: John Ogness
Date: Mon Nov 07 2022 - 09:19:52 EST


Use srcu console list iteration for console list traversal.

Document why the console_lock is still necessary. Note that this
is a preparatory change for when console_lock no longer provides
synchronization for the console list.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
---
kernel/printk/printk.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ec50777d0301..d8ccb7b523e2 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3480,6 +3480,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
struct console *c;
u64 last_diff = 0;
u64 printk_seq;
+ int cookie;
u64 diff;
u64 seq;

@@ -3490,9 +3491,15 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
for (;;) {
diff = 0;

+ /*
+ * Hold the console_lock to guarantee safe access to
+ * console->seq and to prevent changes to @console_suspended
+ * until all consoles have been processed.
+ */
console_lock();

- for_each_console(c) {
+ cookie = console_srcu_read_lock();
+ for_each_console_srcu(c) {
if (con && con != c)
continue;
if (!console_is_usable(c))
@@ -3501,6 +3508,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
if (printk_seq < seq)
diff += seq - printk_seq;
}
+ console_srcu_read_unlock(cookie);

/*
* If consoles are suspended, it cannot be expected that they
--
2.30.2