netdev - Re: [PATCH v2 bpf-next 3/4] bpf: Allow using bpf_sk_storage in FENTRY/FEXIT/RAW

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Message-ID: <20201116100004.1bc5e70e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 16 Nov 2020 10:00:04 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Martin KaFai Lau <kafai@...com>
Cc:     <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        <netdev@...r.kernel.org>, Song Liu <songliubraving@...com>
Subject: Re: [PATCH v2 bpf-next 3/4] bpf: Allow using bpf_sk_storage in
 FENTRY/FEXIT/RAW_TP

On Mon, 16 Nov 2020 09:37:34 -0800 Martin KaFai Lau wrote:
> On Sat, Nov 14, 2020 at 05:17:20PM -0800, Jakub Kicinski wrote:
> > On Thu, 12 Nov 2020 13:13:13 -0800 Martin KaFai Lau wrote:  
> > > This patch adds bpf_sk_storage_get_tracing_proto and
> > > bpf_sk_storage_delete_tracing_proto.  They will check
> > > in runtime that the helpers can only be called when serving
> > > softirq or running in a task context.  That should enable
> > > most common tracing use cases on sk.  
> >   
> > > +	if (!in_serving_softirq() && !in_task())  
> > 
> > This is a curious combination of checks. Would you mind indulging me
> > with an explanation?  
> The current lock usage in bpf_local_storage.c is only expected to
> run in either of these contexts.

:)

Locks that can run in any context but preempt disabled or softirq
disabled?

Let me cut to the chase. Are you sure you didn't mean to check
if (irq_count()) ?