[RFC][PATCH 2/2] printk: take console_sem when accessing console drivers list

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

We need to take console_sem lock when we iterate console
drivers list. Otherwise, another CPU can concurrently
modify console drivers list or console drivers.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 kernel/printk/printk.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index b0e361ca1bea..c2bccf58d03e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2674,12 +2674,17 @@ void register_console(struct console *newcon)
 	struct console_cmdline *c;
 	static bool has_preferred;
 
-	if (console_drivers)
-		for_each_console(bcon)
-			if (WARN(bcon == newcon,
-					"console '%s%d' already registered\n",
-					bcon->name, bcon->index))
-				return;
+	console_lock();
+	if (console_drivers) {
+		for_each_console(bcon) {
+			if (bcon != newcon)
+				continue;
+			WARN(1, "console '%s%d' already registered\n",
+			     bcon->name, bcon->index);
+			console_unlock();
+			return;
+		}
+	}
 
 	/*
 	 * before we register a new CON_BOOT console, make sure we don't
@@ -2691,6 +2696,7 @@ void register_console(struct console *newcon)
 			if (!(bcon->flags & CON_BOOT)) {
 				pr_info("Too late to register bootconsole %s%d\n",
 					newcon->name, newcon->index);
+				console_unlock();
 				return;
 			}
 		}
@@ -2701,6 +2707,7 @@ void register_console(struct console *newcon)
 
 	if (!has_preferred || bcon || !console_drivers)
 		has_preferred = preferred_console >= 0;
+	console_unlock();
 
 	/*
 	 *	See if we want to use this console driver. If we
-- 
2.21.0