Re: swp_pager_meta_build DoS printf

On Monday, August 13, 2012 1:49:38 am Sergey Kandaurov wrote:
> On 2 July 2012 20:31, Bjoern A. Zeeb <bzeeb-lists_at_lists.zabbadoz.net> wrote:
> >
> > On 2. Jul 2012, at 14:36 , John Baldwin wrote:
> >
> >> On Sunday, July 01, 2012 8:23:31 am Bjoern A. Zeeb wrote:
> >>> Hey,
> >>>
> >>> hitting this printf in swp_pager_meta_build()
> >>>
> >>>                        if (uma_zone_exhausted(swap_zone)) {
> >>>                                printf("swap zone exhausted, increase 
kern.maxswzone\n");
> >>>                                vm_pageout_oom(VM_OOM_SWAPZ);
> >>>                                pause("swzonex", 10);
> >>>                        } else
> >>>
> >>> seems to be an effective way to put the machine into a state of no 
recovery
> >>> unless the memory situation would be able to clear itself.  Not that it 
wouldn't
> >>> otherwise be any better but in addition having a couple of tenthousands 
of these
> >>> going to console as well is really not helpful to try to do anything 
either.  Can
> >>> we make it a log() call or something?
> >>>
> >>> /bz
> >>>
> >>> PS: I am not sure as I have seen it on someone else's machines and it's
> >>> probably been ZFS that caused it.  I unfortunately neither had a way to
> >>> get back in or break to a kernel debugger, so information is sparse.
> >>
> >> This used to be a silent deadlock before I added the printf() and the 
call to
> >> OOM. :-P  Do you just want to ratelimit the printf?  We have an API to 
ratelimit
> >> printf's already.
> >
> > Ratelimit would be fine;  I was writing that on the wrong time of the 
wrong day to
> > just get it out;  could you do that?
> 
> Hi, looks like the discussion was abandoned.
> What about this patch? It enables to ratelimit the printf.
> Also, are the new variables put in the right places from the style pov?

I think DES has a newer variant of this now?

-- 
John Baldwin