Net grant tables breaking multiple nic domU

Net grant tables breaking multiple nic domU

[Jerone Young]

While working Bugzilla #183 I figured out what was the problem... Net
grant tables...something that is marked as DANGEROUS in the kernel
config...is on by default. When net grant tables is compiled in bringing
up two interfaces in a domU crashes the domU kernel. But when I compile
both Dom0 & DomU without net grant tables I am able to use two
interfaces in domU with no problem. I don't know a lot about net grant
tables but could someone who know more about net grant tables take a
look at this?

			
-- 
Jerone Young
IBM Linux Technology Center
jyoung5@us.ibm.com
512-838-1157 (T/L: 678-1157)

Re: Net grant tables breaking multiple nic domU

[Nivedita Singhvi]

Jerone Young wrote:
> While working Bugzilla #183 I figured out what was the problem... Net
> grant tables...something that is marked as DANGEROUS in the kernel
> config...is on by default. When net grant tables is compiled in bringing
> up two interfaces in a domU crashes the domU kernel. But when I compile
> both Dom0 & DomU without net grant tables I am able to use two
> interfaces in domU with no problem. I don't know a lot about net grant
> tables but could someone who know more about net grant tables take a
> look at this?
> 
> 			
Jerone,

Did you not see Jim Dykman's updates and posts on this bug?
He's found the root cause, and is putting together a patch,
although some of it might be interim because it exposes
another resource shortage which will have to be addressed
somehow. Expect a patch from him in the next day or two,
and see the bugzilla entry (and previous posts on xen-devel)
from Jim for the details.

thanks,
Nivedita

Re: Net grant tables breaking multiple nic domU

[Jerone Young]

On Tue, 2005-09-13 at 13:50 -0700, Nivedita Singhvi wrote:
> Jerone Young wrote:
> > While working Bugzilla #183 I figured out what was the problem... Net
> > grant tables...something that is marked as DANGEROUS in the kernel
> > config...is on by default. When net grant tables is compiled in bringing
> > up two interfaces in a domU crashes the domU kernel. But when I compile
> > both Dom0 & DomU without net grant tables I am able to use two
> > interfaces in domU with no problem. I don't know a lot about net grant
> > tables but could someone who know more about net grant tables take a
> > look at this?
> > 
> > 			
> Jerone,
> 
> Did you not see Jim Dykman's updates and posts on this bug?
> He's found the root cause, and is putting together a patch,
> although some of it might be interim because it exposes
> another resource shortage which will have to be addressed
> somehow. Expect a patch from him in the next day or two,
> and see the bugzilla entry (and previous posts on xen-devel)
> from Jim for the details.

Yes I did see this. But if that is the case then why does disabling net
grant tables fix the problem? So I just decided to come to the list to
see if someone understanding the net grant table code might know.


> 
> thanks,
> Nivedita
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> 
-- 
Jerone Young
IBM Linux Technology Center
jyoung5@us.ibm.com
512-838-1157 (T/L: 678-1157)

Re: Net grant tables breaking multiple nic domU

[Nivedita Singhvi]

Jerone Young wrote:

>>Did you not see Jim Dykman's updates and posts on this bug?
>>He's found the root cause, and is putting together a patch,
>>although some of it might be interim because it exposes
>>another resource shortage which will have to be addressed
>>somehow. Expect a patch from him in the next day or two,
>>and see the bugzilla entry (and previous posts on xen-devel)
>>from Jim for the details.
> 
> 
> Yes I did see this. But if that is the case then why does disabling net
> grant tables fix the problem? So I just decided to come to the list to
> see if someone understanding the net grant table code might know.

The cause he identified is in the net grant code, so
there is no conflict here, is there?  When you disable
the net grant code, it doesn't use net grant tables,
but falls back to the earlier code, which doesn't have
the bug. Yes, we could disable the net grant stuff, but
as we discussed in previous threads on this list, that
is a temporary workaround, and since this is the code
we want to ship in 3.0, I see the correct thing to do is
to find and fix the real problem, which Jim is doing.

thanks,
Nivedita

RE: Net grant tables breaking multiple nic domU

[Ian Pratt]

> The cause he identified is in the net grant code, so there is 
> no conflict here, is there?  When you disable the net grant 
> code, it doesn't use net grant tables, but falls back to the 
> earlier code, which doesn't have the bug. Yes, we could 
> disable the net grant stuff, but as we discussed in previous 
> threads on this list, that is a temporary workaround, and 
> since this is the code we want to ship in 3.0, I see the 
> correct thing to do is to find and fix the real problem, 
> which Jim is doing.

Yep, its just a case of dynamically allocating more grant table slots
when an interface is brought up. The current BUG failure is needlessly
severe. 

Ian