linux-kernel - Re: [RFC PATCH 6/8] preempt/dynamic: Provide preempt_schedule[

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Message-ID: <20210126235730.lgfa2uida5se5urn@treble>
Date:   Tue, 26 Jan 2021 17:57:30 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Michal Hocko <mhocko@...e.com>,
        rostedt@...dmis.org, jbaron@...mai.com, ardb@...nel.org
Subject: Re: [RFC PATCH 6/8] preempt/dynamic: Provide
 preempt_schedule[_notrace]() static calls

On Fri, Jan 22, 2021 at 05:52:26PM +0100, Peter Zijlstra wrote:
>  static int static_call_add_module(struct module *mod)
>  {
> -	return __static_call_init(mod, mod->static_call_sites,
> -				  mod->static_call_sites + mod->num_static_call_sites);
> +	struct static_call_site *start = mod->static_call_sites;
> +	struct static_call_site *stop = start + mod->num_static_call_sites;
> +	struct static_call_site *site;
> +
> +	for (site = start; site != stop; site++) {
> +		unsigned long addr = (unsigned long)static_call_key(site);
> +		struct static_call_ass *ass;
> +
> +		/*
> +		 * Gotta fix up the keys that point to the trampoline.
> +		 */
> +		if (!kernel_text_address(addr))
> +			continue;
> +
> +		ass = static_call_find_ass(addr);
> +		if (!ass) {
> +			pr_warn("Failed to fixup __raw_static_call() usage at: %ps\n",
> +				static_call_addr(site));
> +			return -EINVAL;
> +		}
> +		site->key = ((unsigned long)ass->key - (unsigned long)&site->key) |
> +			    (site->key & STATIC_CALL_SITE_FLAGS);

Well, I hate it, but I'm not sure I have any better ideas.  It should be
possible to use kallsyms, instead of the rb-tree/register nonsense.  Not
sure about the performance impact though.  Might be a good reason to
speed up kallsyms!

Also I do have some naming suggestions ;-)

-- 
Josh