Re: [PATCH net-next v2 2/3] net: dev: Makes sure netif_rx() can be invoked in any context.

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Jakub Kicinski <kuba@kernel.org>
Cc: bpf@vger.kernel.org, netdev@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Toke Høiland-Jørgensen" <toke@toke.dk>
Subject: Re: [PATCH net-next v2 2/3] net: dev: Makes sure netif_rx() can be invoked in any context.
Date: Thu, 10 Feb 2022 20:52:37 +0100	[thread overview]
Message-ID: <YgVtBQdHZdvrzQp7@linutronix.de> (raw)
In-Reply-To: <20220210101330.47165ae0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

On 2022-02-10 10:13:30 [-0800], Jakub Kicinski wrote:
> > So we do netif_rx_backlog() with the bh disable+enable and
> > __netif_rx_backlog() without it and export both tree wide?
> 
> At a risk of confusing people about the API we could also name the
> "non-super-optimized" version netif_rx(), like you had in your patch.
> Grepping thru the drivers there's ~250 uses so maybe we don't wanna
> touch all that code. No strong preference, I just didn't expect to 
> see __netif_rx_backlog(), but either way works.

So let me keep the naming as-is, export __netif_rx() and update the
kernel doc with the bits about backlog.
After that if we are up to rename the function in ~250 drivers then I
should be simpler.

> > It would make it more obvious indeed. Could we add
> > 	WARN_ON_ONCE(!(hardirq_count() | softirq_count()))
> > to the shortcut to catch the "you did it wrong folks"? This costs me
> > about 2ns.
> 
> Modulo lockdep_..(), so we don't have to run this check on prod kernels?

I was worried a little about the corner cases but then lockdep is your
friend and you should test your code. Okay.

Sebastian