netdev - Re: [PATCH bpf-next v2 07/11] bpf, sockmap: Return socket cookie on lookup from syscall

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Date:   Mon, 13 Jan 2020 19:16:29 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Martin Lau <kafai@...com>, Jakub Sitnicki <jakub@...udflare.com>
Cc:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-team@...udflare.com" <kernel-team@...udflare.com>,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [PATCH bpf-next v2 07/11] bpf, sockmap: Return socket cookie on
 lookup from syscall

Martin Lau wrote:
> On Fri, Jan 10, 2020 at 11:50:23AM +0100, Jakub Sitnicki wrote:
> > Tooling that populates the SOCKMAP with sockets from user-space needs a way
> > to inspect its contents. Returning the struct sock * that SOCKMAP holds to
> > user-space is neither safe nor useful. An approach established by
> > REUSEPORT_SOCKARRAY is to return a socket cookie (a unique identifier)
> > instead.
> > 
> > Since socket cookies are u64 values SOCKMAP needs to support such a value
> > size for lookup to be possible. This requires special handling on update,
> > though. Attempts to do a lookup on SOCKMAP holding u32 values will be met
> > with ENOSPC error.
> > 
> > Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> > ---

[...]
 
> > +static void *sock_map_lookup_sys(struct bpf_map *map, void *key)
> > +{
> > +	struct sock *sk;
> > +
> > +	WARN_ON_ONCE(!rcu_read_lock_held());
> It seems unnecessary.  It is only called by syscall.c which
> holds the rcu_read_lock().  Other than that,
> 

+1 drop it. The normal rcu annotations/splats should catch anything here.

> Acked-by: Martin KaFai Lau <kafai@...com>