netdev - skb_attempt_defer_free and reference counting

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Message-ID: <E3B93E31-3C03-4DAF-A9ED-69523A82E583@akamai.com>
Date: Fri, 31 Oct 2025 11:04:20 +0000
From: "Hudson, Nick" <nhudson@...mai.com>
To: Eric Dumazet <edumazet@...gle.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: skb_attempt_defer_free and reference counting

Hi,

I’ve been looking at using skb_attempt_defer_free and had a question about the skb reference counting.

The existing reference release for any skb handed to skb_attempt_defer_free is done in skb_defer_free_flush (via napi_consume_skb). However, it seems to me that calling skb_attempt_defer_free on the same skb to drop the multiple references is problematic as, if the defer_list isn’t serviced between the calls, the list gets corrupted. That is, the skb can’t appear on the list twice.

Would it be possible to move the reference count drop into skb_attempt_defer_free and only add the skb to the list on last reference drop?

Thanks,
Nick
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