On Wed, 1 Jun 2022, Mikulas Patocka wrote:
>
>
> On Tue, 31 May 2022, Helge Deller wrote:
>
> > Mikulas noticed that the parisc kernel crashes in sd_init() if
> > CONFIG_SCHED_MC is enabled.
> > Multicore-scheduling is probably not very useful on parisc, so simply
> > drop this option.
> >
> > Signed-off-by: Helge Deller <deller@xxxxxx>
> > Noticed-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.18
>
> Hi
>
> I think that we should fix the root cause instead of trying to treat the
> symptoms.
>
> Some more testing showed that:
>
> in sd_init: tl->mask(cpu) returns an empty mask
> tl->mask is cpu_coregroup_mask
> in cpu_coregroup_mask: cpu_topology[cpu].core_sibling is an empty mask,
> that gets returned to sd_init
>
> In arch/parisc/kernel/topology.c:
> init_cpu_topology is called before store_cpu_topology, but it depends on
> the variable dualcores_found being set by store_cpu_topology. Thus, it is
> not set.
>
> store_cpu_topology returns if cpuid_topo->core_id != -1, but during boot,
> store_cpu_topology is called before reset_cpu_topology, thus the member
> "core_id" is uninitialized zero and store_cpu_tolopogy does nothing.
>
> If these issues are addrssed, multicore scheduling will work.
I've found that this fixes it.
Mikulas
---
arch/parisc/kernel/topology.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
Index: linux-2.6/arch/parisc/kernel/topology.c
===================================================================
--- linux-2.6.orig/arch/parisc/kernel/topology.c 2022-06-01 15:32:59.000000000 +0200
+++ linux-2.6/arch/parisc/kernel/topology.c 2022-06-01 16:47:36.000000000 +0200
@@ -95,7 +95,8 @@ static struct sched_domain_topology_leve
*/
void __init init_cpu_topology(void)
{
+ reset_cpu_topology();
/* Set scheduler topology descriptor */
- if (dualcores_found)
+ /*if (dualcores_found)*/
set_sched_topology(parisc_mc_topology);
}
