linux-kernel - Re: [PATCH V4 8/9] jump_label: Batch updates if arch supports it

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Date:   Wed, 6 Feb 2019 15:34:18 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Chris von Recklinghausen <crecklin@...hat.com>,
        Jason Baron <jbaron@...mai.com>, Scott Wood <swood@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Clark Williams <williams@...hat.com>, x86@...nel.org
Subject: Re: [PATCH V4 8/9] jump_label: Batch updates if arch supports it

On Mon,  4 Feb 2019 20:59:01 +0100
Daniel Bristot de Oliveira <bristot@...hat.com> wrote:

> --- a/kernel/jump_label.c
> +++ b/kernel/jump_label.c
> @@ -407,6 +407,7 @@ bool jump_label_can_update_check(struct jump_entry *entry, bool init)
>  	return 0;
>  }
>  
> +#ifndef HAVE_JUMP_LABEL_BATCH
>  static void __jump_label_update(struct static_key *key,
>  				struct jump_entry *entry,
>  				struct jump_entry *stop,
> @@ -419,6 +420,34 @@ static void __jump_label_update(struct static_key *key,
>  		}
>  	}
>  }
> +#else
> +static void __jump_label_update(struct static_key *key,
> +				struct jump_entry *entry,
> +				struct jump_entry *stop,
> +				bool init)
> +{
> +	for_each_label_entry(key, entry, stop) {
> +
> +		if (!jump_label_can_update_check(entry, init))
> +			continue;
> +
> +		if (arch_jump_label_transform_queue(entry,
> +						    jump_label_type(entry)))
> +			continue;
> +
> +		/*
> +		 * Queue's overflow: Apply the current queue, and then
> +		 * queue again. If it stills not possible to queue, BUG!
> +		 */
> +		arch_jump_label_transform_apply();
> +		if (!arch_jump_label_transform_queue(entry,
> +						     jump_label_type(entry))) {
> +			BUG();

Please do not relay on BUG(), since in both case (applied or not),
jump_label is not critical for normal operation. I think you should use
WARN_ONCE() here and lock the jump_label so that root user can report it
to us :)

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>