netdev - RE: [PATCH bpf-next 02/14] bpf: net: Avoid sock_setsockopt() taking sk lock when called from bpf

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Message-ID: <381439a429b54e8e8dda848e1d3d306f@AcuMS.aculab.com>
Date:   Wed, 27 Jul 2022 08:36:18 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Martin KaFai Lau' <kafai@...com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "kernel-team@...com" <kernel-team@...com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: RE: [PATCH bpf-next 02/14] bpf: net: Avoid sock_setsockopt() taking
 sk lock when called from bpf

From: Martin KaFai Lau
> Sent: 27 July 2022 07:09
> 
> Most of the codes in bpf_setsockopt(SOL_SOCKET) are duplicated from
> the sock_setsockopt().  The number of supported options are
> increasing ever and so as the duplicated codes.
> 
> One issue in reusing sock_setsockopt() is that the bpf prog
> has already acquired the sk lock.  sockptr_t is useful to handle this.
> sockptr_t already has a bit 'is_kernel' to handle the kernel-or-user
> memory copy.  This patch adds a 'is_bpf' bit to tell if sk locking
> has already been ensured by the bpf prog.

That is a really horrid place to hide an 'is locked' bit.

You'd be better off splitting sock_setsockopt() to add a function
that is called with sk_lock held and the value read.
That would also save the churn of all the callers.

	David

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