netdev - Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice

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Date: Tue, 7 Nov 2023 13:59:40 -0800
From: Mina Almasry <almasrymina@...gle.com>
To: Yunsheng Lin <linyunsheng@...wei.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Shuah Khan <shuah@...nel.org>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>, 
	Shakeel Butt <shakeelb@...gle.com>, Jeroen de Borst <jeroendb@...gle.com>, 
	Praveen Kaligineedi <pkaligineedi@...gle.com>, Willem de Bruijn <willemb@...gle.com>, 
	Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [RFC PATCH v3 04/12] netdev: support binding dma-buf to netdevice

On Mon, Nov 6, 2023 at 11:46 PM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> On 2023/11/6 10:44, Mina Almasry wrote:
> > +
> > +void __netdev_devmem_binding_free(struct netdev_dmabuf_binding *binding)
> > +{
> > +     size_t size, avail;
> > +
> > +     gen_pool_for_each_chunk(binding->chunk_pool,
> > +                             netdev_devmem_free_chunk_owner, NULL);
> > +
> > +     size = gen_pool_size(binding->chunk_pool);
> > +     avail = gen_pool_avail(binding->chunk_pool);
> > +
> > +     if (!WARN(size != avail, "can't destroy genpool. size=%lu, avail=%lu",
> > +               size, avail))
> > +             gen_pool_destroy(binding->chunk_pool);
>
>
> Is there any other place calling the gen_pool_destroy() when the above
> warning is triggered? Do we have a leaking for binding->chunk_pool?
>

gen_pool_destroy BUG_ON() if it's not empty at the time of destroying.
Technically that should never happen, because
__netdev_devmem_binding_free() should only be called when the refcount
hits 0, so all the chunks have been freed back to the gen_pool. But,
just in case, I don't want to crash the server just because I'm
leaking a chunk... this is a bit of defensive programming that is
typically frowned upon, but the behavior of gen_pool is so severe I
think the WARN() + check is warranted here.

> > +
> > +     dma_buf_unmap_attachment(binding->attachment, binding->sgt,
> > +                              DMA_BIDIRECTIONAL);
> > +     dma_buf_detach(binding->dmabuf, binding->attachment);
> > +     dma_buf_put(binding->dmabuf);
> > +     kfree(binding);
> > +}
> > +
>
>


-- 
Thanks,
Mina