On Tue, Oct 19, 2021 at 05:37:27PM +0200, Christian König wrote:

Am 19.10.21 um 14:41 schrieb Daniel Vetter:

quoted

On Tue, Oct 19, 2021 at 08:23:45PM +0800, guangming.cao@mediatek.com wrote:

quoted

From: Guangming Cao <redacted>

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 <redacted>

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.

Well I would call that overkill.

I think if done right the object debug stuff should be able to give you a
backtrace. Which might be useful if you have a dma-buf heaps design where
you really have no clue why a buffer was allocated/attached without some
hints.

quoted

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).

You also don't need the WARN(!list_empty...) because a few line below we
already have a "WARN_ON(!list_empty(&dmabuf->attachments));".

Yeah this patch here alone isn't really that useful I think. Maybe we
could add the dmabuf->exp_name or so to that warning, but otherwise the
info printed here isn't all that useful for debugging. Grabbing a
backtrace of the allocator or attacher otoh should fairly immedialy point
at the buggy code.
-Daniel

Christian.

quoted

-Daniel

quoted

---
  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

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