linux-kernel - Re: [RFC PATCH 01/12] locking/lockdep: Rework lockdep_set_novalidate

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Date:   Sat, 10 Nov 2018 19:26:51 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 01/12] locking/lockdep: Rework
 lockdep_set_novalidate_class()

On 11/10/2018 09:14 AM, Peter Zijlstra wrote:
> On Thu, Nov 08, 2018 at 03:34:17PM -0500, Waiman Long wrote:
>> The current lockdep_set_novalidate_class() implementation is like
>> a hack. It assigns a special class key for that lock and calls
>> lockdep_init_map() twice.
> Ideally it would go away.. it is not thing that should be used.

Yes, I agree. Right now, lockdep_set_novalidate_class() is used in

drivers/base/core.c:    lockdep_set_novalidate_class(&dev->mutex);
drivers/md/bcache/btree.c:      lockdep_set_novalidate_class(&b->lock);
drivers/md/bcache/btree.c:     
lockdep_set_novalidate_class(&b->write_lock);

Do you know the history behind making them novalidate?

>
>> This patch changes the implementation to make it more general so that
>> it can be used by other special lock class types. A new "type" field
>> is added to both the lockdep_map and lock_class structures.
>>
>> The new field can now be used to designate a lock and a class object
>> as novalidate. The lockdep_set_novalidate_class() call, however, should
>> be called before lock initialization which calls lockdep_init_map().
> I don't really feel like this is something that should be made easier or
> better.

I am not saying that this patch make lockdep_set_novalidate_class()
easier to use. It is that terminal locks will share similar code path
and so I rework it so that they can checked together in one test instead
of 2 separate tests.

>> @@ -102,6 +100,8 @@ struct lock_class {
>>  	int				name_version;
>>  	const char			*name;
>>  
>> +	unsigned int			flags;
>> +
>>  #ifdef CONFIG_LOCK_STAT
>>  	unsigned long			contention_point[LOCKSTAT_POINTS];
>>  	unsigned long			contending_point[LOCKSTAT_POINTS];
> Esp. not at the cost of growing the data structures.
>
>

I did reduce the size by 16 bytes for 64-bit architecture in my previous
lockdep patch. Now I claw back 8 bytes for this new functionality.

Cheers,
Longman