[PATCH] make elv_register() output atomic

[PATCH] make elv_register() output atomic

[Thibaut VARENE]

Hi,

Booting 2.6.21-rc3-g45592145 I noticed the following on one of my
machines in the bootlog:

io scheduler noop registered<6>Time: jiffies clocksource has been installed.

io scheduler deadline registered (default)


Looking at block/elevator.c, it appears that elv_register() uses two
consecutive printks in a non-atomic way, leading to the above glitch. The
attached trivial patch fixes this issue, by using a single printk.

HTH

T-Bone

PS: please CC-me in replies.

Signed-off-by: Thibaut VARENE <varenet@parisc-linux.org>

-- 
Thibaut VARENE
http://www.parisc-linux.org/~varenet/


diff --git a/block/elevator.c b/block/elevator.c
index 25f6ef2..96a00c8 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -964,17 +964,18 @@ void elv_unregister_queue(struct request_queue *q)
 
 int elv_register(struct elevator_type *e)
 {
+	char *def = "";
 	spin_lock_irq(&elv_list_lock);
 	BUG_ON(elevator_find(e->elevator_name));
 	list_add_tail(&e->list, &elv_list);
 	spin_unlock_irq(&elv_list_lock);
 
-	printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
 	if (!strcmp(e->elevator_name, chosen_elevator) ||
 			(!*chosen_elevator &&
 			 !strcmp(e->elevator_name, CONFIG_DEFAULT_IOSCHED)))
-				printk(" (default)");
-	printk("\n");
+				def = " (default)";
+
+	printk(KERN_INFO "io scheduler %s registered%s\n", e->elevator_name, def);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(elv_register);

Re: [PATCH] make elv_register() output atomic

[Jens Axboe]

On Thu, Mar 08 2007, Thibaut VARENE wrote:
> Hi,
> 
> Booting 2.6.21-rc3-g45592145 I noticed the following on one of my
> machines in the bootlog:
> 
> io scheduler noop registered<6>Time: jiffies clocksource has been installed.
> 
> io scheduler deadline registered (default)
> 
> 
> Looking at block/elevator.c, it appears that elv_register() uses two
> consecutive printks in a non-atomic way, leading to the above glitch. The
> attached trivial patch fixes this issue, by using a single printk.

Thanks, looks like a good fix!

-- 
Jens Axboe