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    Subject[tip:perfcounters/core] perf_counter: fix nmi-watchdog interaction
    Commit-ID:  63a809a2dc53b91268dd915bbcbd425063893676
    Gitweb: http://git.kernel.org/tip/63a809a2dc53b91268dd915bbcbd425063893676
    Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    AuthorDate: Fri, 1 May 2009 12:23:17 +0200
    Committer: Ingo Molnar <mingo@elte.hu>
    CommitDate: Fri, 1 May 2009 13:23:44 +0200

    perf_counter: fix nmi-watchdog interaction

    When we don't have any perf-counters active, don't act like we know
    what the NMI is for.

    [ Impact: fix hard hang with nmi_watchdog=2 ]

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
    LKML-Reference: <20090501102533.109867793@chello.nl>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>


    ---
    arch/x86/kernel/cpu/perf_counter.c | 3 +++
    1 files changed, 3 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
    index fc06f4d..d4c0cc9 100644
    --- a/arch/x86/kernel/cpu/perf_counter.c
    +++ b/arch/x86/kernel/cpu/perf_counter.c
    @@ -871,6 +871,9 @@ perf_counter_nmi_handler(struct notifier_block *self,
    struct pt_regs *regs;
    int ret;

    + if (!atomic_read(&num_counters))
    + return NOTIFY_DONE;
    +
    switch (cmd) {
    case DIE_NMI:
    case DIE_NMI_IPI:

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