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    Subject[PATCH 5.18 003/879] parisc: fix a crash with multicore scheduler
    Date
    From: Mikulas Patocka <mpatocka@redhat.com>

    commit 6ba688364856ad083be537f08e86ba97f433d405 upstream.

    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@redhat.com>
    Cc: stable@vger.kernel.org # v5.18
    Signed-off-by: Helge Deller <deller@gmx.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/parisc/kernel/processor.c | 2 --
    arch/parisc/kernel/topology.c | 16 +---------------
    2 files changed, 1 insertion(+), 17 deletions(-)

    diff --git a/arch/parisc/kernel/processor.c b/arch/parisc/kernel/processor.c
    index 26eb568f8b96..dddaaa6e7a82 100644
    --- a/arch/parisc/kernel/processor.c
    +++ b/arch/parisc/kernel/processor.c
    @@ -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 */

    diff --git a/arch/parisc/kernel/topology.c b/arch/parisc/kernel/topology.c
    index 9696e3cb6a2a..b9d845e314f8 100644
    --- a/arch/parisc/kernel/topology.c
    +++ b/arch/parisc/kernel/topology.c
    @@ -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 cpuid)
    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 cpuid)
    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();
    }
    --
    2.36.1


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