linux-kernel - Re: [PATCH v19 09/30] drm/shmem-helper: Add and use lockless drm_gem_shmem_get

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Date: Fri, 26 Jan 2024 00:52:19 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: David Airlie <airlied@...il.com>, Gerd Hoffmann <kraxel@...hat.com>,
 Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu
 <olvaffe@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 Christian König <christian.koenig@....com>,
 Qiang Yu <yuq825@...il.com>, Steven Price <steven.price@....com>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Emma Anholt <emma@...olt.net>, Melissa Wen <mwen@...lia.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v19 09/30] drm/shmem-helper: Add and use lockless
 drm_gem_shmem_get_pages()

On 1/25/24 20:24, Daniel Vetter wrote:
> On Fri, Jan 05, 2024 at 09:46:03PM +0300, Dmitry Osipenko wrote:
>> Add lockless drm_gem_shmem_get_pages() helper that skips taking reservation
>> lock if pages_use_count is non-zero, leveraging from atomicity of the
>> refcount_t. Make drm_gem_shmem_mmap() to utilize the new helper.
>>
>> Acked-by: Maxime Ripard <mripard@...nel.org>
>> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
>> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
>> ---
>>  drivers/gpu/drm/drm_gem_shmem_helper.c | 19 +++++++++++++++----
>>  1 file changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> index cacf0f8c42e2..1c032513abf1 100644
>> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
>> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
>> @@ -226,6 +226,20 @@ void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem)
>>  }
>>  EXPORT_SYMBOL_GPL(drm_gem_shmem_put_pages_locked);
>>  
>> +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
>> +{
>> +	int ret;
> 
> Just random drive-by comment: a might_lock annotation here might be good,
> or people could hit some really interesting bugs that are rather hard to
> reproduce ...
> -Sima

Thanks for the suggestion!

-- 
Best regards,
Dmitry