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    SubjectRe: [PATCH] cpuidle: Fix panic in CPU off-lining with no idle driver
    On 04/01/2012 09:07 AM, Toshi Kani wrote:

    > Fix a NULL pointer dereference panic in cpuidle_play_dead() during
    > CPU off-lining when no cpuidle driver is registered. A cpuidle
    > driver may be registered at boot-time based on CPU type. This patch
    > allows an off-lined CPU to enter HLT-based idle in this condition.
    >
    > Signed-off-by: Toshi Kani <toshi.kani@hp.com>
    > Cc: Boris Ostrovsky <boris.ostrovsky@amd.com>
    > ---
    > drivers/cpuidle/cpuidle.c | 5 ++++-
    > 1 files changed, 4 insertions(+), 1 deletions(-)
    >
    > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
    > index 87411ce..2f0083a 100644
    > --- a/drivers/cpuidle/cpuidle.c
    > +++ b/drivers/cpuidle/cpuidle.c
    > @@ -74,7 +74,7 @@ static cpuidle_enter_t cpuidle_enter_ops;
    > /**
    > * cpuidle_play_dead - cpu off-lining
    > *
    > - * Only returns in case of an error
    > + * Returns in case of an error or no driver
    > */
    > int cpuidle_play_dead(void)
    > {
    > @@ -83,6 +83,9 @@ int cpuidle_play_dead(void)
    > int i, dead_state = -1;
    > int power_usage = -1;
    >
    > + if (!drv)
    > + return -ENODEV;
    > +
    > /* Find lowest-power state that supports long-term idle */
    > for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
    > struct cpuidle_state *s = &drv->states[i];



    Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Tested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>


    [The machine I tested on did support mwait. So, to disable mwait and ensure
    that no idle driver is registered, I applied my fix for "idle=" parameters
    (https://lkml.org/lkml/2012/4/3/158) and then passed idle=halt in the kernel
    command line. Then the machine crashed during CPU offline. Then I tried your
    patch and it fixed the issue.]

    Regards,
    Srivatsa S. Bhat
    IBM Linux Technology Center



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