On Tue, Oct 19, 2021 at 08:23:45PM +0800, guangming.cao@xxxxxxxxxxxx wrote:
> From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
>
> Since there is no mandatory inspection for attachments in dma_buf_release.
> There will be a case that dma_buf already released but attachment is still
> in use, which can points to the dmabuf, and it maybe cause
> some unexpected issues.
>
> With IOMMU, when this cases occurs, there will have IOMMU address
> translation fault(s) followed by this warning,
> I think it's useful for dma devices to debug issue.
>
> Signed-off-by: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
This feels a lot like hand-rolling kobject debugging. If you want to do
this then I think adding kobject debug support to
dma_buf/dma_buf_attachment would be better than hand-rolling something
bespoke here.
Also on the patch itself: You don't need the trylock. For correctly
working code non one else can get at the dma-buf, so no locking needed to
iterate through the attachment list. For incorrect code the kernel will be
on fire pretty soon anyway, trying to do locking won't help :-) And
without the trylock we can catch more bugs (e.g. if you also forgot to
unlock and not just forgot to detach).
-Daniel
> ---
> drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 511fe0d217a0..672404857d6a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -74,6 +74,29 @@ static void dma_buf_release(struct dentry *dentry)
> */
> BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);
>
> + /* attachment check */
> + if (dma_resv_trylock(dmabuf->resv) && WARN(!list_empty(&dmabuf->attachments),
> + "%s err, inode:%08lu size:%08zu name:%s exp_name:%s flags:0x%08x mode:0x%08x, %s\n",
> + __func__, file_inode(dmabuf->file)->i_ino, dmabuf->size,
> + dmabuf->name, dmabuf->exp_name,
> + dmabuf->file->f_flags, dmabuf->file->f_mode,
> + "Release dmabuf before detach all attachments, dump attach:\n")) {
> + int attach_cnt = 0;
> + dma_addr_t dma_addr;
> + struct dma_buf_attachment *attach_obj;
> + /* dump all attachment info */
> + list_for_each_entry(attach_obj, &dmabuf->attachments, node) {
> + dma_addr = (dma_addr_t)0;
> + if (attach_obj->sgt)
> + dma_addr = sg_dma_address(attach_obj->sgt->sgl);
> + pr_err("attach[%d]: dev:%s dma_addr:0x%-12lx\n",
> + attach_cnt, dev_name(attach_obj->dev), dma_addr);
> + attach_cnt++;
> + }
> + pr_err("Total %d devices attached\n\n", attach_cnt);
> + dma_resv_unlock(dmabuf->resv);
> + }
> +
> dmabuf->ops->release(dmabuf);
>
> if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
> --
> 2.17.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
