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From: Jakub Sitnicki <jakub@cloudflare.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: daniel@iogearbox.net, lmb@isovalent.com, edumazet@google.com,
	bpf@vger.kernel.org, netdev@vger.kernel.org, ast@kernel.org,
	andrii@kernel.org, will@isovalent.com
Subject: Re: [PATCH bpf v6 03/12] bpf: sockmap, improved check for empty queue
Date: Tue, 11 Apr 2023 19:53:51 +0200	[thread overview]
Message-ID: <87pm8agv8y.fsf@cloudflare.com> (raw)
In-Reply-To: <20230407171654.107311-4-john.fastabend@gmail.com>

On Fri, Apr 07, 2023 at 10:16 AM -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 also check the 'state' variable where we would cache partially
> processed sk_buff. This catches the majority of cases. But, we also
> need to use the mutex lock around this check because we can't have both
> codes running and check sensibly. We could perhaps do this with atomic
> bit checks, but we are already here due to memory pressure so slowing
> things down a bit seems OK and simpler to just grab a lock.
>
> 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>
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

  reply	other threads:[~2023-04-11 17:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-04-07 17:16 [PATCH bpf v6 00/12] bpf sockmap fixes John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 01/12] bpf: sockmap, pass skb ownership through read_skb John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 02/12] bpf: sockmap, convert schedule_work into delayed_work John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 03/12] bpf: sockmap, improved check for empty queue John Fastabend
2023-04-11 17:53   ` Jakub Sitnicki [this message]
2023-04-13 17:51   ` Alexei Starovoitov
2023-04-13 20:06     ` John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 04/12] bpf: sockmap, handle fin correctly John Fastabend
2023-04-11 18:02   ` Jakub Sitnicki
2023-04-07 17:16 ` [PATCH bpf v6 05/12] bpf: sockmap, TCP data stall on recv before accept John Fastabend
2023-04-12 10:26   ` Jakub Sitnicki
2023-04-07 17:16 ` [PATCH bpf v6 06/12] bpf: sockmap, wake up polling after data copy John Fastabend
2023-04-13 13:00   ` Jakub Sitnicki
2023-04-07 17:16 ` [PATCH bpf v6 07/12] bpf: sockmap, incorrectly handling copied_seq John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 08/12] bpf: sockmap, pull socket helpers out of listen test for general use John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 09/12] bpf: sockmap, build helper to create connected socket pair John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 10/12] bpf: sockmap, test shutdown() correctly exits epoll and recv()=0 John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 11/12] bpf: sockmap, test FIONREAD returns correct bytes in rx buffer John Fastabend
2023-04-07 17:16 ` [PATCH bpf v6 12/12] bpf: sockmap, test FIONREAD returns correct bytes in rx buffer with drops John Fastabend

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