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

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Date:   Mon, 16 Nov 2020 10:43:40 -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 10:37:49 -0800 Martin KaFai Lau wrote:
> On Mon, Nov 16, 2020 at 10:00:04AM -0800, Jakub Kicinski wrote:
> > Locks that can run in any context but preempt disabled or softirq
> > disabled?  
> Not exactly. e.g. running from irq won't work.
> 
> > Let me cut to the chase. Are you sure you didn't mean to check
> > if (irq_count()) ?  
> so, no.
> 
> From preempt.h:
> 
> /*
>  * ...
>  * in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled
>  * ...
>  */
> #define in_interrupt()          (irq_count())

Right, as I said in my correction (in_irq() || in_nmi()).

Just to spell it out AFAIU in_serving_softirq() will return true when
softirq is active and interrupted by a hard irq or an NMI.