[patch] as-iosched divide by zero fix

[Robert Love <rml@tech9.net>]

On Wed, 2003-06-11 at 17:24, Andrew Morton wrote:

> Do you know what the actual oops is?

I got it all figured out now.

It is a divide by zero in update_write_batch() called from
as_completed_request().

> Odd that starting the X server triggers it.  Be interesting if your patch
> fixes things for Brian.

I reproduced it without X.

The divide by zero is on line 959 with the divide by 'write_time'. It
can obviously be zero (see line 950). The divide by 'batch' on line 953
seems safe.

The correct patch is below.

Most important question: why are only some of us seeing this?

	Robert Love


Fix as-iosched divide-by-zero bug.

 drivers/block/as-iosched.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)


diff -urN linux-2.5.70-mm8/drivers/block/as-iosched.c linux/drivers/block/as-iosched.c
--- linux-2.5.70-mm8/drivers/block/as-iosched.c	2003-06-11 17:12:02.000000000 -0700
+++ linux/drivers/block/as-iosched.c	2003-06-11 18:04:15.222619392 -0700
@@ -954,9 +954,9 @@
 			ad->write_batch_count /= 2;
 		else
 			ad->write_batch_count--;
-		
+
 	} else if (write_time + 5 < batch && ad->current_write_count == 0) {
-		if (batch / write_time > 2)
+		if (write_time && (batch / write_time > 2))
 			ad->write_batch_count *= 2;
 		else
 			ad->write_batch_count++;