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

[John Ogness]

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