[v18,11/26] drm/shmem-helper: Prepare drm_gem_shmem_free() to shrinker addition

  Prepare drm_gem_shmem_free() to addition of memory shrinker support
to drm-shmem by adding and using variant of put_pages() that doesn't
touch reservation lock. Reservation shouldn't be touched because lockdep
will trigger a bogus warning about locking contention with fs_reclaim
code paths that can't happen during the time when GEM is freed and
lockdep doesn't know about that.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++-------------
 1 file changed, 18 insertions(+), 17 deletions(-)
  

On Mon, 30 Oct 2023 02:01:50 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:

> Prepare drm_gem_shmem_free() to addition of memory shrinker support
> to drm-shmem by adding and using variant of put_pages() that doesn't
> touch reservation lock. Reservation shouldn't be touched because lockdep
> will trigger a bogus warning about locking contention with fs_reclaim
> code paths that can't happen during the time when GEM is freed and
> lockdep doesn't know about that.
> 
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++-------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 08b5a57c59d8..24ff2b99e75b 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -128,6 +128,22 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>  
> +static void
> +drm_gem_shmem_free_pages(struct drm_gem_shmem_object *shmem)
> +{
> +	struct drm_gem_object *obj = &shmem->base;
> +
> +#ifdef CONFIG_X86
> +	if (shmem->map_wc)
> +		set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> +#endif
> +
> +	drm_gem_put_pages(obj, shmem->pages,
> +			  shmem->pages_mark_dirty_on_put,
> +			  shmem->pages_mark_accessed_on_put);
> +	shmem->pages = NULL;
> +}
> +
>  /**
>   * drm_gem_shmem_free - Free resources associated with a shmem GEM object
>   * @shmem: shmem GEM object to free
> @@ -142,8 +158,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  	if (obj->import_attach) {
>  		drm_prime_gem_destroy(obj, shmem->sgt);
>  	} else {
> -		dma_resv_lock(shmem->base.resv, NULL);
> -
>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
>  
>  		if (shmem->sgt) {
> @@ -157,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>  

If you drop the dma_resv_lock/unlock(), you should also replace the
drm_gem_shmem_put_pages_locked() by a drm_gem_shmem_free_pages() in this
commit.

>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count));
>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count));
> -
> -		dma_resv_unlock(shmem->base.resv);
>  	}
>  
>  	drm_gem_object_release(obj);
> @@ -208,21 +220,10 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem)
>   */
>  void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>  {
> -	struct drm_gem_object *obj = &shmem->base;
> -
>  	dma_resv_assert_held(shmem->base.resv);
>  
> -	if (refcount_dec_and_test(&shmem->pages_use_count)) {
> -#ifdef CONFIG_X86
> -		if (shmem->map_wc)
> -			set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> -#endif
> -
> -		drm_gem_put_pages(obj, shmem->pages,
> -				  shmem->pages_mark_dirty_on_put,
> -				  shmem->pages_mark_accessed_on_put);
> -		shmem->pages = NULL;
> -	}
> +	if (refcount_dec_and_test(&shmem->pages_use_count))
> +		drm_gem_shmem_free_pages(shmem);
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
>
  

On 11/10/23 13:16, Boris Brezillon wrote:
> On Mon, 30 Oct 2023 02:01:50 +0300
> Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:
> 
>> Prepare drm_gem_shmem_free() to addition of memory shrinker support
>> to drm-shmem by adding and using variant of put_pages() that doesn't
>> touch reservation lock. Reservation shouldn't be touched because lockdep
>> will trigger a bogus warning about locking contention with fs_reclaim
>> code paths that can't happen during the time when GEM is freed and
>> lockdep doesn't know about that.
>>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>> ---
>>  drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++-------------
>>  1 file changed, 18 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> index 08b5a57c59d8..24ff2b99e75b 100644
>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> @@ -128,6 +128,22 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
>>  }
>>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>>  
>> +static void
>> +drm_gem_shmem_free_pages(struct drm_gem_shmem_object *shmem)
>> +{
>> +	struct drm_gem_object *obj = &shmem->base;
>> +
>> +#ifdef CONFIG_X86
>> +	if (shmem->map_wc)
>> +		set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
>> +#endif
>> +
>> +	drm_gem_put_pages(obj, shmem->pages,
>> +			  shmem->pages_mark_dirty_on_put,
>> +			  shmem->pages_mark_accessed_on_put);
>> +	shmem->pages = NULL;
>> +}
>> +
>>  /**
>>   * drm_gem_shmem_free - Free resources associated with a shmem GEM object
>>   * @shmem: shmem GEM object to free
>> @@ -142,8 +158,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>>  	if (obj->import_attach) {
>>  		drm_prime_gem_destroy(obj, shmem->sgt);
>>  	} else {
>> -		dma_resv_lock(shmem->base.resv, NULL);
>> -
>>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
>>  
>>  		if (shmem->sgt) {
>> @@ -157,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>>  
> If you drop the dma_resv_lock/unlock(), you should also replace the
> drm_gem_shmem_put_pages_locked() by a drm_gem_shmem_free_pages() in this
> commit.

drm_gem_shmem_put_pages_locked() is exported by a later patch of this
series, it's not worthwhile to remove this function
  

On Mon, 20 Nov 2023 14:02:29 +0300
Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:

> On 11/10/23 13:16, Boris Brezillon wrote:
> > On Mon, 30 Oct 2023 02:01:50 +0300
> > Dmitry Osipenko <dmitry.osipenko@collabora.com> wrote:
> >   
> >> Prepare drm_gem_shmem_free() to addition of memory shrinker support
> >> to drm-shmem by adding and using variant of put_pages() that doesn't
> >> touch reservation lock. Reservation shouldn't be touched because lockdep
> >> will trigger a bogus warning about locking contention with fs_reclaim
> >> code paths that can't happen during the time when GEM is freed and
> >> lockdep doesn't know about that.
> >>
> >> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> >> ---
> >>  drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++-------------
> >>  1 file changed, 18 insertions(+), 17 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> index 08b5a57c59d8..24ff2b99e75b 100644
> >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> @@ -128,6 +128,22 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
> >>  }
> >>  EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
> >>  
> >> +static void
> >> +drm_gem_shmem_free_pages(struct drm_gem_shmem_object *shmem)
> >> +{
> >> +	struct drm_gem_object *obj = &shmem->base;
> >> +
> >> +#ifdef CONFIG_X86
> >> +	if (shmem->map_wc)
> >> +		set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> >> +#endif
> >> +
> >> +	drm_gem_put_pages(obj, shmem->pages,
> >> +			  shmem->pages_mark_dirty_on_put,
> >> +			  shmem->pages_mark_accessed_on_put);
> >> +	shmem->pages = NULL;
> >> +}
> >> +
> >>  /**
> >>   * drm_gem_shmem_free - Free resources associated with a shmem GEM object
> >>   * @shmem: shmem GEM object to free
> >> @@ -142,8 +158,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> >>  	if (obj->import_attach) {
> >>  		drm_prime_gem_destroy(obj, shmem->sgt);
> >>  	} else {
> >> -		dma_resv_lock(shmem->base.resv, NULL);
> >> -
> >>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
> >>  
> >>  		if (shmem->sgt) {
> >> @@ -157,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> >>    
> > If you drop the dma_resv_lock/unlock(), you should also replace the
> > drm_gem_shmem_put_pages_locked() by a drm_gem_shmem_free_pages() in this
> > commit.  
> 
> drm_gem_shmem_put_pages_locked() is exported by a later patch of this
> series, it's not worthwhile to remove this function

I'm not talking about removing drm_gem_shmem_put_pages_locked(), but
replacing the drm_gem_shmem_put_pages_locked() call you have in
drm_gem_shmem_free() by a drm_gem_shmem_free_pages(), so you don't end
up with a lockdep warning when you stop exactly here in the patch
series, which is important if we want to keep things bisectable.
  

On 11/20/23 14:19, Boris Brezillon wrote:
...
>>>> -		dma_resv_lock(shmem->base.resv, NULL);
>>>> -
>>>>  		drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
>>>>  
>>>>  		if (shmem->sgt) {
>>>> @@ -157,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
>>>>    
>>> If you drop the dma_resv_lock/unlock(), you should also replace the
>>> drm_gem_shmem_put_pages_locked() by a drm_gem_shmem_free_pages() in this
>>> commit.  
>>
>> drm_gem_shmem_put_pages_locked() is exported by a later patch of this
>> series, it's not worthwhile to remove this function
> 
> I'm not talking about removing drm_gem_shmem_put_pages_locked(), but
> replacing the drm_gem_shmem_put_pages_locked() call you have in
> drm_gem_shmem_free() by a drm_gem_shmem_free_pages(), so you don't end
> up with a lockdep warning when you stop exactly here in the patch
> series, which is important if we want to keep things bisectable.

Indeed, there is assert_locked() there. Thanks for the clarification :)