Hi Mikulas,
On 6/1/22 19:18, Mikulas Patocka wrote:
> With the kernel 5.18, the system will hang on boot if it is compiled with
> CONFIG_SCHED_MC. The last printed message is "Brought up 1 node, 1 CPU".
>
> The crash happens in sd_init
> tl->mask (which is cpu_coregroup_mask) returns an empty mask. This happens
> because cpu_topology[0].core_sibling is empty.
> Consequently, sd_span is set to an empty mask
> sd_id = cpumask_first(sd_span) sets sd_id == NR_CPUS (because the mask is
> empty)
> sd->shared = *per_cpu_ptr(sdd->sds, sd_id); sets sd->shared to NULL
> because sd_id is out of range
> atomic_inc(&sd->shared->ref); crashes without printing anything
>
> We can fix it by calling reset_cpu_topology() from init_cpu_topology() -
> this will initialize the sibling masks on CPUs, so that they're not empty.
>
> This patch also removes the variable "dualcores_found", it is useless,
> because during boot, init_cpu_topology is called before
> store_cpu_topology. Thus, set_sched_topology(parisc_mc_topology) is never
> called. We don't need to call it at all because default_topology in
> kernel/sched/topology.c contains the same items as parisc_mc_topology.
>
> Note that we should not call store_cpu_topology() from init_per_cpu()
> because it is called too early in the kernel initialization process and it
> results in the message "Failure to register CPU0 device". Before this
> patch, store_cpu_topology() would exit immediatelly because
> cpuid_topo->core id was uninitialized and it was 0.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.18
Thanks a lot !!!
It took me some time to test it, but it looks good and boots on
all of my machines so far. I was curious if 32-bit kernels still
work since that was one of the issues with the older patches...
With your patch we can drop the "config SCHED_MC" entry from
arch/parisc/Kconfig as well.
Will you respin, or should I simply add this to your patch?
Helge
>
> ---
> arch/parisc/kernel/processor.c | 2 --
> arch/parisc/kernel/topology.c | 16 +---------------
> 2 files changed, 1 insertion(+), 17 deletions(-)
>
> 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 18:37:37.000000000 +0200
> @@ -20,8 +20,6 @@
>
> static DEFINE_PER_CPU(struct cpu, cpu_devices);
>
> -static int dualcores_found;
> -
> /*
> * store_cpu_topology is called at boot when only one cpu is running
> * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
> @@ -60,7 +58,6 @@ void store_cpu_topology(unsigned int cpu
> if (p->cpu_loc) {
> cpuid_topo->core_id++;
> cpuid_topo->package_id = cpu_topology[cpu].package_id;
> - dualcores_found = 1;
> continue;
> }
> }
> @@ -80,22 +77,11 @@ void store_cpu_topology(unsigned int cpu
> cpu_topology[cpuid].package_id);
> }
>
> -static struct sched_domain_topology_level parisc_mc_topology[] = {
> -#ifdef CONFIG_SCHED_MC
> - { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
> -#endif
> -
> - { cpu_cpu_mask, SD_INIT_NAME(DIE) },
> - { NULL, },
> -};
> -
> /*
> * init_cpu_topology is called at boot when only one cpu is running
> * which prevent simultaneous write access to cpu_topology array
> */
> void __init init_cpu_topology(void)
> {
> - /* Set scheduler topology descriptor */
> - if (dualcores_found)
> - set_sched_topology(parisc_mc_topology);
> + reset_cpu_topology();
> }
> Index: linux-2.6/arch/parisc/kernel/processor.c
> ===================================================================
> --- linux-2.6.orig/arch/parisc/kernel/processor.c 2022-06-01 15:32:59.000000000 +0200
> +++ linux-2.6/arch/parisc/kernel/processor.c 2022-06-01 18:35:12.000000000 +0200
> @@ -327,8 +327,6 @@ int init_per_cpu(int cpunum)
> set_firmware_width();
> ret = pdc_coproc_cfg(&coproc_cfg);
>
> - store_cpu_topology(cpunum);
> -
> if(ret >= 0 && coproc_cfg.ccr_functional) {
> mtctl(coproc_cfg.ccr_functional, 10); /* 10 == Coprocessor Control Reg */
>
>
