Re: [RFC 02/12] staging/android/sync: add sync_fence_create_dma

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 23-11-15 om 14:44 schreef Tvrtko Ursulin:
>
> On 23/11/15 13:38, John Harrison wrote:
>> On 23/11/2015 13:27, Maarten Lankhorst wrote:
>>> Op 23-11-15 om 12:34 schreef John.C.Harrison@Intel.com:
>>>> From: Maarten Lankhorst <maarten.lankhorst@canonical.com>
>>>>
>>>> This allows users of dma fences to create a android fence.
>>>>
>>>> v2: Added kerneldoc. (Tvrtko Ursulin).
>>>>
>>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>>> Cc: Daniel Vetter <daniel@ffwll.ch>
>>>> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
>>>> Cc: devel@driverdev.osuosl.org
>>>> Cc: Riley Andrews <riandrews@android.com>
>>>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>>> Cc: Arve Hjønnevåg <arve@android.com>
>>>> ---
>>>>   drivers/staging/android/sync.c | 13 +++++++++----
>>>>   drivers/staging/android/sync.h | 12 +++++++++++-
>>>>   2 files changed, 20 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/android/sync.c
>>>> b/drivers/staging/android/sync.c
>>>> index f83e00c..7f0e919 100644
>>>> --- a/drivers/staging/android/sync.c
>>>> +++ b/drivers/staging/android/sync.c
>>>> @@ -188,7 +188,7 @@ static void fence_check_cb_func(struct fence *f,
>>>> struct fence_cb *cb)
>>>>   }
>>>>   /* TODO: implement a create which takes more that one sync_pt */
>>>> -struct sync_fence *sync_fence_create(const char *name, struct
>>>> sync_pt *pt)
>>>> +struct sync_fence *sync_fence_create_dma(const char *name, struct
>>>> fence *pt)
>>>>   {
>>>>       struct sync_fence *fence;
>>>> @@ -199,16 +199,21 @@ struct sync_fence *sync_fence_create(const char
>>>> *name, struct sync_pt *pt)
>>>>       fence->num_fences = 1;
>>>>       atomic_set(&fence->status, 1);
>>>> -    fence->cbs[0].sync_pt = &pt->base;
>>>> +    fence->cbs[0].sync_pt = pt;
>>>>       fence->cbs[0].fence = fence;
>>>> -    if (fence_add_callback(&pt->base, &fence->cbs[0].cb,
>>>> -                   fence_check_cb_func))
>>>> +    if (fence_add_callback(pt, &fence->cbs[0].cb, fence_check_cb_func))
>>>>           atomic_dec(&fence->status);
>>>>       sync_fence_debug_add(fence);
>>>>       return fence;
>>>>   }
>>>> +EXPORT_SYMBOL(sync_fence_create_dma);
>>>> +
>>>> +struct sync_fence *sync_fence_create(const char *name, struct
>>>> sync_pt *pt)
>>>> +{
>>>> +    return sync_fence_create_dma(name, &pt->base);
>>>> +}
>>>>   EXPORT_SYMBOL(sync_fence_create);
>>>>   struct sync_fence *sync_fence_fdget(int fd)
>>>> diff --git a/drivers/staging/android/sync.h
>>>> b/drivers/staging/android/sync.h
>>>> index 61f8a3a..798cd56 100644
>>>> --- a/drivers/staging/android/sync.h
>>>> +++ b/drivers/staging/android/sync.h
>>>> @@ -250,10 +250,20 @@ void sync_pt_free(struct sync_pt *pt);
>>>>    * @pt:        sync_pt to add to the fence
>>>>    *
>>>>    * Creates a fence containg @pt.  Once this is called, the fence takes
>>>> - * ownership of @pt.
>>>> + * a reference on @pt.
>>>>    */
>>>>   struct sync_fence *sync_fence_create(const char *name, struct
>>>> sync_pt *pt);
>>> No it doesn't.
>>>> +/**
>>>> + * sync_fence_create_dma() - creates a sync fence from dma-fence
>>>> + * @name:    name of fence to create
>>>> + * @pt:    dma-fence to add to the fence
>>>> + *
>>>> + * Creates a fence containg @pt.  Once this is called, the fence takes
>>>> + * a reference on @pt.
>>>> + */
>>> No it doesn't.
>> This is your patch isn't it? Or is this something Tvrtko added on the
>> way past? Either way, what should the correct description be? It takes a
>
> It is Maarten's patch, I just copied the comment over from one function to another. The one I picked up was https://patchwork.freedesktop.org/patch/38074/, December 2014.
>
>> copy of the pointer to 'pt'. Is the comment meaning a reference in the
>> sense of 'pass by reference', i.e. a pointer? But you are meaning a
>> reference in the sense of incrementing a usage count?
>
> Maybe he means it is still taking ownership, not reference?
Indeed. See commit 3ea411c56ef "android: fix reference leak in sync_fence_create".

This broke compatibility with android by creating a ref leak. :)

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