Re: [PATCH] cpuidle: Fix panic in CPU off-lining with no idle driver

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

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