Re: [PATCH v2 2/8] media: videobuf2: Make bufs array dynamic allocated

[Tomasz Figa <tfiga@chromium.org>]

On Tue, Mar 21, 2023 at 08:16:10PM +0200, Laurent Pinchart wrote:
> Hi Benjamin,
> 
> Thank you for the patch.
> 
> On Tue, Mar 21, 2023 at 11:28:49AM +0100, Benjamin Gaignard wrote:
> > Instead of a static array change bufs to a dynamically allocated array.
> > This will allow to store more video buffer if needed.
> > Protect the array with a spinlock.
> 
> I think I asked in the review of v1 why we couldn't use the kernel
> IDA/IDR APIs to allocate buffer IDs and register buffers, but I don't
> think I've received a reply. Wouldn't it be better than rolling out our
> own mechanism ?
> 

+1, with a note that [1] suggests that IDR is deprecated and XArray[2]
should be used instead.

[1] https://docs.kernel.org/core-api/idr.html
[2] https://docs.kernel.org/core-api/xarray.html

Also from my quick look, XArray may be solving the locking concerns for us
automatically.

Best regards,
Tomasz

> > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> > ---
> >  .../media/common/videobuf2/videobuf2-core.c   |  8 +++
> >  include/media/videobuf2-core.h                | 49 ++++++++++++++++---
> >  2 files changed, 49 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > index 79e90e338846..ae9d72f4d181 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -2452,6 +2452,13 @@ int vb2_core_queue_init(struct vb2_queue *q)
> >  	mutex_init(&q->mmap_lock);
> >  	init_waitqueue_head(&q->done_wq);
> >  
> > +	q->max_num_bufs = 32;
> > +	q->bufs = kmalloc_array(q->max_num_bufs, sizeof(*q->bufs), GFP_KERNEL | __GFP_ZERO);
> > +	if (!q->bufs)
> > +		return -ENOMEM;
> > +
> > +	spin_lock_init(&q->bufs_lock);
> > +
> >  	q->memory = VB2_MEMORY_UNKNOWN;
> >  
> >  	if (q->buf_struct_size == 0)
> > @@ -2479,6 +2486,7 @@ void vb2_core_queue_release(struct vb2_queue *q)
> >  	mutex_lock(&q->mmap_lock);
> >  	__vb2_queue_free(q, q->num_buffers);
> >  	mutex_unlock(&q->mmap_lock);
> > +	kfree(q->bufs);
> >  }
> >  EXPORT_SYMBOL_GPL(vb2_core_queue_release);
> >  
> > diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
> > index 5b1e3d801546..397dbf6e61e1 100644
> > --- a/include/media/videobuf2-core.h
> > +++ b/include/media/videobuf2-core.h
> > @@ -558,6 +558,8 @@ struct vb2_buf_ops {
> >   * @dma_dir:	DMA mapping direction.
> >   * @bufs:	videobuf2 buffer structures
> >   * @num_buffers: number of allocated/used buffers
> > + * @bufs_lock: lock to protect bufs access
> > + * @max_num_bufs: max number of buffers storable in bufs
> >   * @queued_list: list of buffers currently queued from userspace
> >   * @queued_count: number of buffers queued and ready for streaming.
> >   * @owned_by_drv_count: number of buffers owned by the driver
> > @@ -619,8 +621,10 @@ struct vb2_queue {
> >  	struct mutex			mmap_lock;
> >  	unsigned int			memory;
> >  	enum dma_data_direction		dma_dir;
> > -	struct vb2_buffer		*bufs[VB2_MAX_FRAME];
> > +	struct vb2_buffer		**bufs;
> >  	unsigned int			num_buffers;
> > +	spinlock_t			bufs_lock;
> > +	size_t				max_num_bufs;
> >  
> >  	struct list_head		queued_list;
> >  	unsigned int			queued_count;
> > @@ -1239,9 +1243,16 @@ static inline void vb2_clear_last_buffer_dequeued(struct vb2_queue *q)
> >  static inline struct vb2_buffer *vb2_get_buffer(struct vb2_queue *q,
> >  						unsigned int index)
> >  {
> > -	if (index < q->num_buffers)
> > -		return q->bufs[index];
> > -	return NULL;
> > +	struct vb2_buffer *vb = NULL;
> > +
> > +	spin_lock(&q->bufs_lock);
> > +
> > +	if (index < q->max_num_bufs)
> > +		vb = q->bufs[index];
> > +
> > +	spin_unlock(&q->bufs_lock);
> > +
> > +	return vb;
> >  }
> >  
> >  /**
> > @@ -1251,12 +1262,30 @@ static inline struct vb2_buffer *vb2_get_buffer(struct vb2_queue *q,
> >   */
> >  static inline bool vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb)
> >  {
> > -	if (vb->index < VB2_MAX_FRAME) {
> > +	bool ret = false;
> > +
> > +	spin_lock(&q->bufs_lock);
> > +
> > +	if (vb->index >= q->max_num_bufs) {
> > +		struct vb2_buffer **tmp;
> > +
> > +		tmp = krealloc_array(q->bufs, q->max_num_bufs * 2, sizeof(*q->bufs), GFP_KERNEL);
> > +		if (!tmp)
> > +			goto realloc_failed;
> > +
> > +		q->max_num_bufs *= 2;
> > +		q->bufs = tmp;
> > +	}
> > +
> > +	if (vb->index < q->max_num_bufs) {
> >  		q->bufs[vb->index] = vb;
> > -		return true;
> > +		ret = true;
> >  	}
> >  
> > -	return false;
> > +realloc_failed:
> > +	spin_unlock(&q->bufs_lock);
> > +
> > +	return ret;
> >  }
> >  
> >  /**
> > @@ -1266,8 +1295,12 @@ static inline bool vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *
> >   */
> >  static inline void vb2_queue_remove_buffer(struct vb2_queue *q, struct vb2_buffer *vb)
> >  {
> > -	if (vb->index < VB2_MAX_FRAME)
> > +	spin_lock(&q->bufs_lock);
> > +
> > +	if (vb->index < q->max_num_bufs)
> >  		q->bufs[vb->index] = NULL;
> > +
> > +	spin_unlock(&q->bufs_lock);
> >  }
> >  
> >  /*
> 
> -- 
> Regards,
> 
> Laurent Pinchart