[PATCH printk v3 15/40] kdb: use srcu console list iterator

[John Ogness]

Guarantee safe iteration of the console list by using SRCU.

Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
 kernel/debug/kdb/kdb_io.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 550fe8b456ec..ed8289ce4fcb 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -545,6 +545,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
 {
 	struct console *c;
 	const char *cp;
+	int cookie;
 	int len;
 
 	if (msg_len == 0)
@@ -558,7 +559,15 @@ static void kdb_msg_write(const char *msg, int msg_len)
 		cp++;
 	}
 
-	for_each_console(c) {
+	/*
+	 * The console_srcu_read_lock() only provides safe console list
+	 * traversal. The use of the ->write() callback relies on all other
+	 * CPUs being stopped at the moment and console drivers being able to
+	 * handle reentrance when @oops_in_progress is set. (Note that there
+	 * is no guarantee for either criteria.)
+	 */
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(c) {
 		if (!console_is_enabled(c))
 			continue;
 		if (c == dbg_io_ops->cons)
@@ -577,6 +586,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
 		--oops_in_progress;
 		touch_nmi_watchdog();
 	}
+	console_srcu_read_unlock(cookie);
 }
 
 int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
-- 
2.30.2