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Message-ID: <ddcae9fe-6155-4542-898c-bfb06e8721b8@collabora.com>
Date: Fri, 26 Jan 2024 00:52:19 +0300
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Subject: Re: [PATCH v19 09/30] drm/shmem-helper: Add and use lockless
 drm_gem_shmem_get_pages()
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To: David Airlie <airlied@gmail.com>, Gerd Hoffmann <kraxel@redhat.com>,
 Gurchetan Singh <gurchetansingh@chromium.org>, Chia-I Wu
 <olvaffe@gmail.com>, Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
 Maxime Ripard <mripard@kernel.org>, Thomas Zimmermann <tzimmermann@suse.de>,
 =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
 Qiang Yu <yuq825@gmail.com>, Steven Price <steven.price@arm.com>,
 Boris Brezillon <boris.brezillon@collabora.com>,
 Emma Anholt <emma@anholt.net>, Melissa Wen <mwen@igalia.com>,
 dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
 kernel@collabora.com, virtualization@lists.linux-foundation.org
References: <20240105184624.508603-1-dmitry.osipenko@collabora.com>
 <20240105184624.508603-10-dmitry.osipenko@collabora.com>
 <ZbKZNCbZoV4ovWTH@phenom.ffwll.local>
From: Dmitry Osipenko <dmitry.osipenko@collabora.com>
In-Reply-To: <ZbKZNCbZoV4ovWTH@phenom.ffwll.local>
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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@kernel.org>
>> Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
>> Suggested-by: Boris Brezillon <boris.brezillon@collabora.com>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.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