netdev - Re: [PATCH net-next V2 2/2] net: kfree_skb_list use kmem_cache_free

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Date:   Thu, 19 Jan 2023 11:17:58 +0100
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     brouer@...hat.com, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>, edumazet@...gle.com,
        pabeni@...hat.com
Subject: Re: [PATCH net-next V2 2/2] net: kfree_skb_list use
 kmem_cache_free_bulk



On 19/01/2023 03.26, Jakub Kicinski wrote:
> On Wed, 18 Jan 2023 22:37:47 +0100 Jesper Dangaard Brouer wrote:
>>> +		skb_mark_not_on_list(segs);
>>
>> The syzbot[1] bug goes way if I remove this skb_mark_not_on_list().
>>
>> I don't understand why I cannot clear skb->next here?
> 
> Some of the skbs on the list are not private?
> IOW we should only unlink them if skb_unref().

Yes, you are right.

The skb_mark_not_on_list() should only be called if __kfree_skb_reason()
returns true, meaning the SKB is ready to be free'ed (as it calls/check
skb_unref()).

I will send a proper fix patch shortly... after syzbot do a test on it.

--Jesper