Re: [Xen-devel] irqbalance seg faults with 2.6.38 or later kernels [patch + solution included] if running under Xen hypervisor

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, May 11, 2011 at 09:16:53AM +0100, Jan Beulich wrote:
> >>> On 11.05.11 at 02:33, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >>> wrote:
> > The reason behind it is that irqbalance parses the /proc/interrupts
> > and whenever it hits something it can't understand:
> > 
> >  RES:  191614137   73904910    Rescheduling interrupts
> > 
> > It will count the number of interrupts towards the IRQ 0. That IRQ does 
> > exist
> > when the kernel boots under baremetal:
> > 
> >   0:         46          0       IO-APIC-edge      timer
> > 
> > but under Xen, the timer interrupts are initialized much later:
> > 
> >  272:   41197188          0        xen-percpu-virq      timer0
> > 
> > and the first IRQ that is used is not zero, but rather one:
> > 
> >    1:      73037          0          0          0          0          0  
> > xen-pirq-ioapic-edge  i8042
> > 
> > so when irqbalance tries to account for the IRQ 'RES' to the IRQ 0
> > it fails and segfaults. The attached patch fixes it for whoever else is
> > hitting this problem.
> 
> In the svn snapshot I have, I see
> 
>               /* lines with letters in front are special, like NMI count. 
> Ignore */
>               if (!(line[0]==' ' || (line[0]>='0' && line[0]<='9')))
>                       break;
> 
> which I would think should be taking care of your problem (or
> I mis-read your description), and which was there already before

Not anymore. In kernels 2.6.37:

           CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       
.. snip.
NMI:          0          0          0          0   Non-maskable interrupts
LOC:   12413629   12858323   16296183   11098466   Local timer interrupts

In 2.6.38 and later:
            CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       
 TRM:          0          0          0          0          0          0   
Thermal event interrupts
 THR:          0          0          0          0          0          0   
Threshold APIC interrupts
 MCE:          0          0          0          0          0          0   
Machine check exceptions

They added in a space before the name. The check you mentioned
above could be augmented for this of course, as another solution
for this.

> 0.56. Or are you perhaps having the problem because you have
> 1000+ interrupts, thus causing even the non-numeric strings to
> get space padded on their left? In that case I'd rather think above
> check should be either improved or removed (replaced by your
> solution).
> 
> > I am not sure who the upstream maintainer is for this so
> > I am sending this patch to the different distros as well.
> 
> Copying Neil and Arjan.
> 
> Jan
> 
> > 
> > --- irqbalance-0.56.orig/procinterrupts.c   2010-06-10 10:45:55.000000000 
> > -0400
> > +++ irqbalance-0.56/procinterrupts.c        2011-05-10 20:22:06.897465003 
> > -0400
> > @@ -50,7 +50,7 @@ void parse_proc_interrupts(void)
> >             int cpunr;
> >             int      number;
> >             uint64_t count;
> > -           char *c, *c2;
> > +           char *c, *c2, *err;
> >  
> >             if (getline(&line, &size, file)==0)
> >                     break;
> > @@ -64,7 +64,11 @@ void parse_proc_interrupts(void)
> >                     continue;
> >             *c = 0;
> >             c++;
> > -           number = strtoul(line, NULL, 10);
> > +           number = strtoul(line, &err, 10);
> > +           /* Man page says that if that happens and number == 0, then it
> > +            * failed to parse. */
> > +           if (err == line && number == 0)
> > +                   continue;
> >             count = 0;
> >             cpunr = 0;
> >  
> 
> 

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