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    Subject[tip:smp/hotplug] perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode()
    Commit-ID:  494d8679788930b29e1262d92db4c1912bdf9119
    Gitweb: http://git.kernel.org/tip/494d8679788930b29e1262d92db4c1912bdf9119
    Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    AuthorDate: Tue, 18 Apr 2017 19:04:58 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Thu, 20 Apr 2017 13:08:55 +0200

    perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode()

    If intel_snb_check_microcode() is invoked via
    microcode_init -> perf_check_microcode -> intel_snb_check_microcode

    then get_online_cpus() is invoked nested. This works with the current
    implementation of get_online_cpus() but prevents converting it to a percpu
    rwsem.

    intel_snb_check_microcode() is also invoked from intel_sandybridge_quirk()
    unprotected.

    Drop get_online_cpus() from intel_snb_check_microcode() and add it to
    intel_sandybridge_quirk() so both call sites are protected.

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Borislav Petkov <bp@suse.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Link: http://lkml.kernel.org/r/20170418170553.713742599@linutronix.de

    ---
    arch/x86/events/intel/core.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
    index eb1484c..152b7e4 100644
    --- a/arch/x86/events/intel/core.c
    +++ b/arch/x86/events/intel/core.c
    @@ -3389,12 +3389,10 @@ static void intel_snb_check_microcode(void)
    int pebs_broken = 0;
    int cpu;

    - get_online_cpus();
    for_each_online_cpu(cpu) {
    if ((pebs_broken = intel_snb_pebs_broken(cpu)))
    break;
    }
    - put_online_cpus();

    if (pebs_broken == x86_pmu.pebs_broken)
    return;
    @@ -3467,7 +3465,9 @@ static bool check_msr(unsigned long msr, u64 mask)
    static __init void intel_sandybridge_quirk(void)
    {
    x86_pmu.check_microcode = intel_snb_check_microcode;
    + get_online_cpus();
    intel_snb_check_microcode();
    + put_online_cpus();
    }

    static const struct { int id; char *name; } intel_arch_events_map[] __initconst = {
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