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Subject[patch] as-iosched divide by zero fix
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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++;


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