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From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "David S. Miller"
 <davem@davemloft.net>, Boqun Feng <boqun.feng@gmail.com>, Daniel Borkmann
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 Waiman Long <longman@redhat.com>, Will Deacon <will@kernel.org>, Alexei
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 Stanislav Fomichev <sdf@google.com>, Yonghong Song
 <yonghong.song@linux.dev>, bpf@vger.kernel.org
Subject: Re: [PATCH net-next 14/15] net: Reference bpf_redirect_info via
 task_struct on PREEMPT_RT.
In-Reply-To: <20240507105731.bjCHl0YH@linutronix.de>
References: <20240503182957.1042122-1-bigeasy@linutronix.de>
 <20240503182957.1042122-15-bigeasy@linutronix.de> <87y18mohhp.fsf@toke.dk>
 <20240507105731.bjCHl0YH@linutronix.de>
Date: Tue, 07 May 2024 15:50:49 +0200
Message-ID: <874jb9ohmu.fsf@toke.dk>
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Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:

>> > +static inline struct bpf_redirect_info *bpf_net_ctx_get_ri(void)
>> > +{
>> > +	struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
>> > +
>> > +	if (!bpf_net_ctx)
>> > +		return NULL;
>> 
>> ... do we really need all the NULL checks?
>> 
>> (not just here, but in the code below as well).
>> 
>> I'm a little concerned that we are introducing a bunch of new branches
>> in the XDP hot path. Which is also why I'm asking for benchmarks :)
>
> We could hide the WARN behind CONFIG_DEBUG_NET. The only purpose is to
> see the backtrace where the context is missing. Having just an error
> somewhere will make it difficult to track.
>
> The NULL check is to avoid a crash if the context is missing. You could
> argue that this should be noticed in development and never hit
> production. If so, then we get the backtrace from NULL-pointer
> dereference and don't need the checks and WARN.

Yup, this (relying on the NULL deref) SGTM :)

-Toke