Re: 4.5-rc4 kernel is failed to bootup on CN6880

[David Daney]

On 02/22/2016 11:15 AM, Yang Shi wrote:
> On 2/22/2016 4:43 AM, Aaro Koskinen wrote:
> > Hi,
> >
> > On Fri, Feb 19, 2016 at 05:12:41PM -0800, Yang Shi wrote:
> > > I tried to boot 4.5-rc4 kernel on my CN6880 board, but it is failed at
> > > booting up secondary cores. The error is:
> > With v4.5-rc5, EBB6800 is booting fine:
> >
> > [    0.000000] CPU0 revision is: 000d9108 (Cavium Octeon II)
> > [...]
> > [ 2286.273935] SMP: Booting CPU01 (CoreId  1)...
> > [ 2286.278201] CPU1 revision is: 000d9108 (Cavium Octeon II)
> > [...]
> > [ 2287.214953] SMP: Booting CPU31 (CoreId 31)...
> > [ 2287.224668] CPU31 revision is: 000d9108 (Cavium Octeon II)
> > [ 2287.224865] Brought up 32 CPUs
> >
> > > CPU31 revision is: 000d9101 (Cavium Octeon II)
> > > SMP: Booting CPU32 (CoreId 32)...
> > > Secondary boot timeout
> > >
> > > I passed "numcores=32" in kernel commandline since there are 32 cores
> > > ion
> > > CN6880.
> > You shouldn't have CPU32 in that case, the numbering starts from zero.
> > Also the coremask is 32-bit.
> >
> > I can reproduce your issue with CONFIG_NR_CPUS=64. Possibly this code
> > is incorrect for NR_CPUS bigger than 32:
> >
> >          /* The present CPUs get the lowest CPU numbers. */
> >          cpus = 1;
> >          for (id = 0; id < NR_CPUS; id++) {
> >                  if ((id != coreid) && (core_mask & (1 << id))) {
> >                          set_cpu_possible(cpus, true);
> >                          set_cpu_present(cpus, true);
> >
> > What CONFIG_NR_CPUS did you use?
>
> Thanks. I did have 48 NR_CPUS set. It works when I changed it to 32.
>
> I think the problem is core_mask is 32 bit. But when NR_CPUS > 32, in
> "core_mask & (1 << id)" core_mask will be sign extended, then the
> statement will return non-zero all the time.

That is correct, and perhaps not coincidentally, the reason I have 
already submitted patches to fix this.

David.


> Yang
>
> > A.