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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> 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
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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