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    Subject[PATCH v4] x86, hotplug: fix llc shared map unreleased during cpu hotplug
    Date
    BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
    IP: [..] find_busiest_group
    PGD 5a9d5067 PUD 13067 PMD 0
    Oops: 0000 [#3] SMP
    [...]
    Call Trace:
    load_balance
    ? _raw_spin_unlock_irqrestore
    idle_balance
    __schedule
    schedule
    schedule_timeout
    ? lock_timer_base
    schedule_timeout_uninterruptible
    msleep
    lock_device_hotplug_sysfs
    online_store
    dev_attr_store
    sysfs_write_file
    vfs_write
    SyS_write
    system_call_fastpath

    Last level cache shared map is built during cpu up and build sched domain
    routine takes advantage of it to setup sched domain cpu topology, however,
    llc shared map is unreleased during cpu disable which lead to invalid sched
    domain cpu topology. This patch fix it by release llc shared map correctly
    during cpu disable.

    Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
    Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
    ---
    v1 -> v2:
    * fix subject line
    v2 -> v3:
    * simplify backtrace

    arch/x86/kernel/smpboot.c | 3 +++
    1 file changed, 3 insertions(+)

    diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
    index 5492798..0134ec7 100644
    --- a/arch/x86/kernel/smpboot.c
    +++ b/arch/x86/kernel/smpboot.c
    @@ -1292,6 +1292,9 @@ static void remove_siblinginfo(int cpu)

    for_each_cpu(sibling, cpu_sibling_mask(cpu))
    cpumask_clear_cpu(cpu, cpu_sibling_mask(sibling));
    + for_each_cpu(sibling, cpu_llc_shared_mask(cpu))
    + cpumask_clear_cpu(cpu, cpu_llc_shared_mask(sibling));
    + cpumask_clear(cpu_llc_shared_mask(cpu));
    cpumask_clear(cpu_sibling_mask(cpu));
    cpumask_clear(cpu_core_mask(cpu));
    c->phys_proc_id = 0;
    --
    1.9.1


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