RE: [Xen-devel] xend crash/hang scenario

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> It seems that any large 
> output of 
> binary to the console will hang xend. I can reproduce the 
> exact situation 
> with "cat /usr/bin/vim" or any other decent-sized binary.  
> Xend managed to 
> recover from cat-ing binaries up to about 1.5mb, but anything 
> larger than 2mb 
> had xend using 99% cpu anywhere from 5 minutes to 
> indefinitely (longer than I 
> could wait anyway). 

Yep, fixing this has been on the todo list for a while. 
I'm surprised its taken someone so long to spot it :-)

We need to limit the rate at which xend is prepared to take message off
a given control ring. There'll then be back pressure to the domain,
which can either choose to block or throw away messages. 

> In contrast to the binary output, even extremely large text 
> files (500mb+) 
> appear to have no ill effect, even when cat'd in a while loop.

I think you're just getting lucky. At least I can't think why there'd be
a difference between binary and text, unless xend does some scanning of
the console messages I'm not aware of.
 
> I have not tried outside of my setup so I don't know if it's 
> reproducable, but 
> it is very concerning to me that any user in any domain 
> could, with a typo, 
> crush the CPU and take out all management capability as well. 
>  I'll provide 
> any additional info if it will help.

Yep, this is serious and needs fixing. Volunteers?

Thanks,
Ian


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