linux-kernel - Re: [PATCH 3/3] static_call: Fix static_call

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Date:   Thu, 18 Mar 2021 11:13:08 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, jbaron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, linux-kernel@...r.kernel.org,
        sumit.garg@...aro.org, oliver.sang@...el.com, jarkko@...nel.org
Subject: Re: [PATCH 3/3] static_call: Fix static_call_update() sanity check

On Thu, Mar 18, 2021 at 12:31:59PM +0100, Peter Zijlstra wrote:
>  			if (!kernel_text_address((unsigned long)site_addr)) {
> -				WARN_ONCE(1, "can't patch static call site at %pS",
> +				/*
> +				 * This skips patching __exit, which is part of
> +				 * init_section_contains() but is not part of
> +				 * kernel_text_address().
> +				 *
> +				 * Skipping __exit is fine since it will never
> +				 * be executed.
> +				 */
> +				WARN_ONCE(!static_call_is_init(site),
> +					  "can't patch static call site at %pS",
>  					  site_addr);
>  				continue;
>  			}

It might be good to clarify the situation for __exit in modules in the
comment and/or changelog, as they both seem to be implicitly talking
only about __exit in vmlinux.

For CONFIG_MODULE_UNLOAD, the code ends up in the normal text area, so
static_call_is_init() is false and kernel_text_address() is true.

For !CONFIG_MODULE_UNLOAD, the code gets discarded during module load,
so static_call_is_init() and kernel_text_address() are both false.  I
guess that will trigger a warning?

-- 
Josh