linux-kernel - Re: [PATCH v1 1/2] dma-buf: Make locking consistent in dma_buf

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Date:   Thu, 27 Oct 2022 08:13:38 +0200
From:   Christian König <christian.koenig@....com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, noralf@...nnes.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] dma-buf: Make locking consistent in
 dma_buf_detach()

Am 27.10.22 um 00:46 schrieb Dmitry Osipenko:
> The dma_buf_detach() locks attach->dmabuf->resv and then unlocks
> dmabuf->resv, which could be a two different locks from a static
> code checker perspective. In particular this triggers Smatch to
> report the "double unlock" error. Make the locking pointers consistent.
>
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Link: https://lore.kernel.org/dri-devel/Y1fLfsccW3AS%2Fo+%2F@kili/
> Fixes: 809d9c72c2f8 ("dma-buf: Move dma_buf_attach() to dynamic locking specification")
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

It would be even cleaner if we completely drop the dmabuf parameter for 
the function and just use the inside the attachment.

Anyway patch is Reviewed-by: Christian König <christian.koenig@....com> 
for now, wider cleanups can come later on.

Regards,
Christian.

> ---
>   drivers/dma-buf/dma-buf.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index c40d72d318fd..6e33ef4fde34 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -998,9 +998,10 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>   	if (WARN_ON(!dmabuf || !attach))
>   		return;
>   
> -	dma_resv_lock(attach->dmabuf->resv, NULL);
> +	dma_resv_lock(dmabuf->resv, NULL);
>   
>   	if (attach->sgt) {
> +		WARN_ON(dmabuf != attach->dmabuf);
>   
>   		__unmap_dma_buf(attach, attach->sgt, attach->dir);
>