netdev - Re: [RFC] Add BPF_SYNCHRONIZE bpf(2) command

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Message-ID: <CAKOZueu37C49TGny85_LZ_yp+NgQtWfjpBU0CB7OS6HFF-CeHA@mail.gmail.com>
Date:   Fri, 27 Jul 2018 12:17:37 -0700
From:   Daniel Colascione <dancol@...gle.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Lorenzo Colitti <lorenzo@...gle.com>,
        Chenbo Feng <fengc@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Alexei Starovoitov <ast@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Tim Murray <timmurray@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [RFC] Add BPF_SYNCHRONIZE bpf(2) command

On Sat, Jul 14, 2018 at 11:18 AM, Joel Fernandes <joel@...lfernandes.org>
wrote:

> By the way just curious I was briefly going through kernel/bpf/arraymap.c.
> How are you protecting against load-store tearing of values of array map
> updates/lookups?
>
> For example, if userspace reads an array map at a particular index, while
> another CPU is updating it, then userspace can read partial values /
> half-updated values right? Since rcu_read_lock is in use, I was hoping to
> find something like rcu_assign_pointer there to protect readers against
> concurrent updates.  Thanks for any clarification.


I'm also curious about the answer to this question.

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