Re: [patch] numa: fix BUILD_BUG_ON for node_read_distance

[David Rientjes]

On Wed, 10 Mar 2010, Greg KH wrote:

> > node_read_distance() has a BUILD_BUG_ON() to prevent buffer overruns when
> > the number of nodes printed will exceed the buffer length.
> > 
> > Each node only needs four chars: three for distance (maximum distance is
> > 255) and one for a seperating space or a trailing newline.
> 
> Is this causing a problem as-is today that we need to resolve for
> 2.6.34?  Or is this 2.6.35 material?
> 

It's not needed at least for x86 for 2.6.34 since the max 
CONFIG_NODES_SHIFT is 9.  I don't know about other architectures with 
different ranges or page sizes.

I'm going to push a change to the x86 maintainers to increase that max 
CONFIG_NODES_SHIFT to 10 hopefully for 2.6.35, that's where we run into 
this error.

> Who chose this original number, and why is it off by 1/2?
> 

It's earlier than the git history, but there's no reason to divide 
PAGE_SIZE in half.  We've been running machines with this patch for well 
over a year and /sys/devices/system/node/nodeN/distance works just fine 
with 1K nodes.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/