Re: [PATCH] Allow memory hotplug and hibernation in the same kernel

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 13 Nov 2009 11:59:44 +0100
Andi Kleen <andi@firstfloor.org> wrote:

> Allow memory hotplug and hibernation in the same kernel
> 
> Memory hotplug and hibernation was excluded in Kconfig. This is obviously
> a problem for distribution kernels who want to support both in the same
> image.
> 
> After some discussions with Rafael and others the only problem is 
> with parallel memory hotadd or removal while a hibernation operation
> is in process. It was also working for s390 before.
> 
> This patch removes the Kconfig level exclusion, and simply
> makes the memory add / remove functions grab the pm_mutex
> to exclude against hibernation.
> 
> ...
>
> +extern struct mutex pm_mutex;

Am a bit worried by the new mutex.

>  #ifndef CONFIG_HIBERNATION
>  static inline void register_nosave_region(unsigned long b, unsigned long e)
>  {
> @@ -308,8 +310,23 @@ static inline void register_nosave_regio
>  static inline void register_nosave_region_late(unsigned long b, unsigned long e)
>  {
>  }
> -#endif
>  
> -extern struct mutex pm_mutex;
> +static inline void lock_hibernation(void) {}
> +static inline void unlock_hibernation(void) {}
> +
> +#else
> +
> +/* Let some subsystems like memory hotadd exclude hibernation */
> +
> +static inline void lock_hibernation(void)
> +{
> +	mutex_lock(&pm_mutex);
> +}
> +
> +static inline void unlock_hibernation(void)
> +{
> +	mutex_unlock(&pm_mutex);
> +}
> +#endif

Has this been carefully reviewed and lockdep-tested to ensure that we
didn't introduce any ab/ba nasties?