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    Subject[PATCH v5 26/45] perf/x86: Use get/put_online_cpus_atomic() to prevent CPU offline
    Date
    The CPU_DYING notifier modifies the per-cpu pointer pmu->box, and this can
    race with functions such as uncore_pmu_to_box() and uncore_pci_remove() when
    we remove stop_machine() from the CPU offline path. So protect them using
    get/put_online_cpus_atomic().

    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: x86@kernel.org
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    ---

    arch/x86/kernel/cpu/perf_event_intel_uncore.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
    index b43200d..6faae53 100644
    --- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
    +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
    @@ -1,3 +1,4 @@
    +#include <linux/cpu.h>
    #include "perf_event_intel_uncore.h"

    static struct intel_uncore_type *empty_uncore[] = { NULL, };
    @@ -1965,6 +1966,7 @@ uncore_pmu_to_box(struct intel_uncore_pmu *pmu, int cpu)
    if (box)
    return box;

    + get_online_cpus_atomic();
    raw_spin_lock(&uncore_box_lock);
    list_for_each_entry(box, &pmu->box_list, list) {
    if (box->phys_id == topology_physical_package_id(cpu)) {
    @@ -1974,6 +1976,7 @@ uncore_pmu_to_box(struct intel_uncore_pmu *pmu, int cpu)
    }
    }
    raw_spin_unlock(&uncore_box_lock);
    + put_online_cpus_atomic();

    return *per_cpu_ptr(pmu->box, cpu);
    }
    @@ -2556,6 +2559,7 @@ static void uncore_pci_remove(struct pci_dev *pdev)
    if (WARN_ON_ONCE(phys_id != box->phys_id))
    return;

    + get_online_cpus_atomic();
    raw_spin_lock(&uncore_box_lock);
    list_del(&box->list);
    raw_spin_unlock(&uncore_box_lock);
    @@ -2569,6 +2573,7 @@ static void uncore_pci_remove(struct pci_dev *pdev)

    WARN_ON_ONCE(atomic_read(&box->refcnt) != 1);
    kfree(box);
    + put_online_cpus_atomic();
    }

    static int uncore_pci_probe(struct pci_dev *pdev,


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