From: Jakub Sitnicki <jakub@cloudflare.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: daniel@iogearbox.net, bpf@vger.kernel.org,
netdev@vger.kernel.org, edumazet@google.com, ast@kernel.org,
andrii@kernel.org, will@isovalent.com
Subject: Re: [PATCH bpf v8 04/13] bpf: sockmap, improved check for empty queue
Date: Wed, 17 May 2023 11:44:51 +0200 [thread overview]
Message-ID: <87mt238f6j.fsf@cloudflare.com> (raw)
In-Reply-To: <20230517052244.294755-5-john.fastabend@gmail.com>
On Tue, May 16, 2023 at 10:22 PM -07, John Fastabend wrote:
> We noticed some rare sk_buffs were stepping past the queue when system was
> under memory pressure. The general theory is to skip enqueueing
> sk_buffs when its not necessary which is the normal case with a system
> that is properly provisioned for the task, no memory pressure and enough
> cpu assigned.
>
> But, if we can't allocate memory due to an ENOMEM error when enqueueing
> the sk_buff into the sockmap receive queue we push it onto a delayed
> workqueue to retry later. When a new sk_buff is received we then check
> if that queue is empty. However, there is a problem with simply checking
> the queue length. When a sk_buff is being processed from the ingress queue
> but not yet on the sockmap msg receive queue its possible to also recv
> a sk_buff through normal path. It will check the ingress queue which is
> zero and then skip ahead of the pkt being processed.
>
> Previously we used sock lock from both contexts which made the problem
> harder to hit, but not impossible.
>
> To fix instead of popping the skb from the queue entirely we peek the
> skb from the queue and do the copy there. This ensures checks to the
> queue length are non-zero while skb is being processed. Then finally
> when the entire skb has been copied to user space queue or another
> socket we pop it off the queue. This way the queue length check allows
> bypassing the queue only after the list has been completely processed.
>
> To reproduce issue we run NGINX compliance test with sockmap running and
> observe some flakes in our testing that we attributed to this issue.
>
> Fixes: 04919bed948dc ("tcp: Introduce tcp_read_skb()")
> Tested-by: William Findlay <will@isovalent.com>
> Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
next prev parent reply other threads:[~2023-05-17 9:45 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-17 5:22 [PATCH bpf v8 00/13] bpf sockmap fixes John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 01/13] bpf: sockmap, pass skb ownership through read_skb John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 02/13] bpf: sockmap, convert schedule_work into delayed_work John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 03/13] bpf: sockmap, reschedule is now done through backlog John Fastabend
2023-05-17 9:12 ` Jakub Sitnicki
2023-05-17 5:22 ` [PATCH bpf v8 04/13] bpf: sockmap, improved check for empty queue John Fastabend
2023-05-17 9:44 ` Jakub Sitnicki [this message]
2023-05-17 5:22 ` [PATCH bpf v8 05/13] bpf: sockmap, handle fin correctly John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 06/13] bpf: sockmap, TCP data stall on recv before accept John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 07/13] bpf: sockmap, wake up polling after data copy John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 08/13] bpf: sockmap, incorrectly handling copied_seq John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 09/13] bpf: sockmap, pull socket helpers out of listen test for general use John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 10/13] bpf: sockmap, build helper to create connected socket pair John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 11/13] bpf: sockmap, test shutdown() correctly exits epoll and recv()=0 John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 12/13] bpf: sockmap, test FIONREAD returns correct bytes in rx buffer John Fastabend
2023-05-17 5:22 ` [PATCH bpf v8 13/13] bpf: sockmap, test FIONREAD returns correct bytes in rx buffer with drops John Fastabend
2023-05-17 13:54 ` [PATCH bpf v8 00/13] bpf sockmap fixes Daniel Borkmann
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