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

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Date:   Wed, 6 Feb 2019 16:59:42 +0100
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
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>,
        "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 2/6/19 7:34 AM, Masami Hiramatsu wrote:
> 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 :)

Oops! I wrote a patch changing this, removing the BUG(). It was a request from
steve, but somehow I ended up missing it.

Thanks for reviewing this...

My bad, sorry :-(

-- Daniel
> Thank you,
> 
>