netdev - Returning negative values repeatedly from a SOCK

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Message-ID: <4RZ8dWmGaDHrnGI9qP6fnpa2uTfn8K2AWmMOkikYrT8c-L_1Rym92dEjoFhoXop6lwC4C69CNVTteY6SuGg-ymq3WsJ5b64SL0r9r0jIVwk=@protonmail.com>
Date: Sat, 22 Jun 2024 12:15:17 +0000
From: Zac Ecob <zacecob@...tonmail.com>
To: "bpf@...r.kernel.org" <bpf@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Returning negative values repeatedly from a SOCK_FILTER ebpf prog stalls kernel thread

Problem is title. Attached is files for repro. Working on v6.10-rc4. 

After doing some investigation, the `sk_wmem_alloc` member of `struct sk` seems to only be increasing, presumably missing some refcnt_dec somewhere.

At a certain point, in `sock_alloc_send_pskb`, we fail the check:

`
if (sk_wmem_alloc_get(sk) < READ_ONCE(sk->sk_sndbuf))
`

Upon which we enter `sock_wait_for_wmem` and schedule a massive timeout (at least that's what happened in my tests)

Please let me know if I need to add anything.

Thanks
Not sure where the missing refcnt subs are, must admit unfamiliarity with the network code.

Download attachment "repro.tar.xz" of type "application/x-xz" (2172 bytes)