netdev - Re: [PATCH net-next v6 1/4] selftests: fix OOM problem in msg

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Message-ID: <66816dc388821_e2572949a@willemb.c.googlers.com.notmuch>
Date: Sun, 30 Jun 2024 10:37:55 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: zijianzhang@...edance.com, 
 netdev@...r.kernel.org
Cc: edumazet@...gle.com, 
 willemdebruijn.kernel@...il.com, 
 cong.wang@...edance.com, 
 xiaochun.lu@...edance.com, 
 Zijian Zhang <zijianzhang@...edance.com>
Subject: Re: [PATCH net-next v6 1/4] selftests: fix OOM problem in
 msg_zerocopy selftest

zijianzhang@ wrote:
> From: Zijian Zhang <zijianzhang@...edance.com>
> 
> In selftests/net/msg_zerocopy.c, it has a while loop keeps calling sendmsg
> on a socket with MSG_ZEROCOPY flag, and it will recv the notifications
> until the socket is not writable. Typically, it will start the receiving
> process after around 30+ sendmsgs. However, because of the
> commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
> the sender is always writable and does not get any chance to run recv
> notifications. The selftest always exits with OUT_OF_MEMORY because the
> memory used by opt_skb exceeds the core.sysctl_optmem_max.
> 
> According to our experiments, this problem can be mitigated by open the
> DEBUG_LOCKDEP configuration for the kernel. But it will makes the
> notifications disordered even in good commits before
> commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale").

Since this is not a real fix, no need to suggest it.
 
> We introduce "cfg_notification_limit" to force sender to receive
> notifications after some number of sendmsgs. And, notifications may not
> come in order, because of the reason we present above. We have order
> checking code managed by cfg_verbose.
> 
> Signed-off-by: Zijian Zhang <zijianzhang@...edance.com>
> Signed-off-by: Xiaochun Lu <xiaochun.lu@...edance.com>

Probably just send this as a separate patch to net-next.