On Tue, 2019-03-12 at 16:17 -0700, Evan Green wrote:

On Tue, Mar 12, 2019 at 7:21 AM Matthias Brugger [off-list ref] wrote:

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On 05/03/2019 20:03, Evan Green wrote:

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On Wed, Feb 27, 2019 at 6:33 AM Yong Wu [off-list ref] wrote:

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On Mon, 2019-02-25 at 15:53 -0800, Evan Green wrote:

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On Mon, Dec 31, 2018 at 8:52 PM Yong Wu [off-list ref] wrote:

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DL_FLAG_AUTOREMOVE_CONSUMER/SUPPLIER means "Remove the link
automatically on consumer/supplier driver unbind", that means we should
remove whole the device_link when there is no this driver no matter what
the ref_count of the link is.

CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Yong Wu <yong.wu@mediatek.com>
---
The ref_count of our device_link normally is over 1. When the consumer
device driver is removed, whole the device_link should be removed.
Thus, I add this patch.
---

I will admit to reading about device links for the first time while
reviewing this patch, but I don't really get this. Why use a kref at
all if we're just going to ignore its value? For instance, I see that
if you call device_link_add() with the same supplier and consumer, it
uses the kref to return the same link. That machinery is broken with
your change. Although I don't see any uses of it, you might also
expect a supplier or consumer could do a kref_get() on the link it got
back from device_link_add(), and have a reasonable expectation that
the link wouldn't be freed out from under it. This would also be
broken.

Can you explain why your device_links normally have a reference count

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1,

I use device link between the smi-larb device and the iommu-consumer
device. Take a example, smi-larb1 have 4 VDEC ports. From 4/13 in this
patchset, we use device_link to link the VDEC device and the smi-larb1
device in the function(mtk_iommu_config). since there are 4 ports, it
will call device_link_add 4 times.

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and why those additional references can't be cleaned up in an
orderly fashion?

If the iommu-consume device(like VDEC above) is removed, It should enter
device_links_driver_cleanup which only ref_put one time. I guess whole
the link should be removed at that time.

It seems like Robin had some suggestions about using
mtk_iommu_add_device() rather than the attach_dev() to set the links
up, and then track them for removal in the corresponding
remove_device() callback. Then you wouldn't need this change, right?

Hi Evan,  sorry for reply you so late. I have not got time to try
this(Put it in the add_device), But I guess it works.
At that time the ref_cnt here should be 1, then this patch is
unnecessary.

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FYI, Evan the patch is queued for v5.1-rc1 as
0fe6f7874d46 ("driver core: Remove the link if there is no driver with AUTO flag")

So if you think there is something wrong with it, then please provide a fix or
raise awareness :)

Oh. Thanks for the heads-up Matthias. It's pretty weird that we have
the kref there whose count we just completely ignore. I'll try to find
some time to submit a patch.

Thanks very much if you improve this.

-Evan

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