linux-kernel - Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch

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Message-ID: <20210904102430.GD4323@worktop.programming.kicks-ass.net>
Date:   Sat, 4 Sep 2021 12:24:30 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Song Liu <songliubraving@...com>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper
 bpf_get_branch_snapshot

On Fri, Sep 03, 2021 at 10:10:16AM -0700, Andrii Nakryiko wrote:
> > I suppose you have to have this helper function because the JIT cannot
> > emit static_call()... although in this case one could cheat and simply
> > emit a call to static_call_query() and not bother with dynamic updates
> > (because there aren't any).
> 
> If that's safe, let's do it.

I'll try and remember to look into static_call_lock(), a means of
forever denying future static_call_update() calls. That should make this
more obvious.