[Intel-gfx] [PATCH] drm/i915/pmu: Initialise our dynamic sysfs attributes for use with lockdep

[Tvrtko Ursulin]

On 11/01/2018 14:04, Chris Wilson wrote:
> As we kmalloc our dynamic sysfs attributes, we have to give them an
> external static lock_class_key for them to use with lockdep.
> 
> Fixes: 109ec558370f ("drm/i915/pmu: Only enumerate available counters in sysfs")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/i915_pmu.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
> index 9139bc8df82b..95ab5e28f5be 100644
> --- a/drivers/gpu/drm/i915/i915_pmu.c
> +++ b/drivers/gpu/drm/i915/i915_pmu.c
> @@ -719,6 +719,7 @@ static const struct attribute_group *i915_pmu_attr_groups[] = {
>   static struct i915_ext_attribute *
>   add_i915_attr(struct i915_ext_attribute *attr, const char *name, u64 config)
>   {
> +	sysfs_attr_init(&attr->attr.attr);
>   	attr->attr.attr.name = name;
>   	attr->attr.attr.mode = 0444;
>   	attr->attr.show = i915_pmu_event_show;
> @@ -731,6 +732,7 @@ static struct perf_pmu_events_attr *
>   add_pmu_attr(struct perf_pmu_events_attr *attr, const char *name,
>   	     const char *str)
>   {
> +	sysfs_attr_init(&attr->attr.attr);
>   	attr->attr.attr.name = name;
>   	attr->attr.attr.mode = 0444;
>   	attr->attr.show = perf_event_sysfs_show;
> 

You beat me to it, after I noticed the report on IRC and started 
digging, just to find sysfs_attr_init, your fix arrived. Thanks!

It looks like a standard way of silencing lockdep for this case, 
although I am not sure what exactly is the purpose of lock class keys in 
sysfs attributes, and what this kind of defeat could also imply.

I planned to do it another loop, iterating the attr array, but I don't 
see how it matters. It would be one static key versus the two. :?

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko