netdev - Returning negative values repeatedly from a SOCK

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Message-ID: <CJrradVmkT-HM6goIYbivHNdWglG0h11_0Ky2ObV_ZCOunJaksIj9alG1UTHCkSDX_Jhm6uB5P5vS8C75QfrjWrqeHisUIDn2023xfv7jp0=@protonmail.com>
Date: Sat, 22 Jun 2024 12:20:05 +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. 

To trigger, I attached an EBPF prof that just returned -1, and send ~1000 packets through it.

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).

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

Please let me know if I need to add anything. 

Thanks