linux-kernel - Re: [RFC][PATCH 0/5] Improve static call NULL handling

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Message-ID: <20230310160952.161d6833@gandalf.local.home>
Date:   Fri, 10 Mar 2023 16:09:52 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Jason Baron <jbaron@...mai.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC][PATCH 0/5] Improve static call NULL handling

On Fri, 10 Mar 2023 12:31:12 -0800
Josh Poimboeuf <jpoimboe@...nel.org> wrote:

>   static_call_update(foo, STATIC_CALL_NOP); // do nothing and return 0
>   static_call_update(foo, STATIC_CALL_BUG); // panic
>   static_call_update(foo, NULL);	    // ???
> 
> The default behavior for NULL could be a key-specific policy, stored as
> a flag in the static_call_key struct.

Could we just get rid of the ambiguity and make

 static_call_update(foo, NULL);

trigger a WARN_ON() instead, and always do nop?

The issue I have with allowing NULL, is that it's not easy to know from the
call site what it does.

-- Steve