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Date:   Wed, 23 Mar 2022 10:12:15 +0800
From:   Hangyu Hua <>
To:     Yasushi SHOJI <>
Cc:     Wolfgang Grandegger <>,
        Marc Kleine-Budde <>,
        David Miller <>,
        Jakub Kicinski <>,
        Vincent Mailhol <>,, Pavel Skripkin <>,,
        linux-can <>,
        netdev <>,
        open list <>
Subject: Re: [PATCH] can: mcba_usb: fix possible double dev_kfree_skb in

Hi yashi,

You are right. There are a series of the same problems about 

This issue was discovered while I was discussing a incorrect patch with 
Marc. You can check this in

So i submitted a new patch. This was the first place where the problem 
occurs. You can check this in


After a week, I realized it could be a series of problems. So
i submitted the following patches


I think this is all affected. None of the four have been merged 
upstream. Do i need to remake all these four patches?


On 2022/3/23 07:08, Yasushi SHOJI wrote:
> Hi Hangyu,
> On Fri, Mar 11, 2022 at 5:02 PM Hangyu Hua <> wrote:
>> There is no need to call dev_kfree_skb when usb_submit_urb fails beacause
>> can_put_echo_skb deletes original skb and can_free_echo_skb deletes the cloned
>> skb.
> So, it's more like, "we don't need to call dev_kfree_skb() after
> can_put_echo_skb()
> because can_put_echo_skb() consumes the given skb.".  It seems it doesn't depend
> on the condition of usb_submit_urb().  Plus, we don't see the "cloned
> skb" at the
> call site.
> Would you mind adding a comment on can_put_echo_skb(), in a separate patch,
> saying the fact that it consumes the skb?
> ems_usb.c, gs_usb.c and possibly some others seem to call
> dev_kfree_skb() as well.
> Are they affected?
> Best,

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