linux-kernel - Re: [PATCH 1/2] locking/lockdep: Cleanup reinit

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Date:   Mon, 14 Feb 2022 15:08:09 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] locking/lockdep: Cleanup reinit_class()

On 2/14/22 06:25, Peter Zijlstra wrote:
> On Thu, Feb 10, 2022 at 10:55:25PM -0500, Waiman Long wrote:
>> Replace the duplicated WARN_ON_ONCE() tests in reinit_class() with
>> BUILD_BUG_ON().
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>>   include/linux/lockdep_types.h | 4 ++++
>>   kernel/locking/lockdep.c      | 6 +++---
>>   2 files changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h
>> index d22430840b53..446d981ae3a2 100644
>> --- a/include/linux/lockdep_types.h
>> +++ b/include/linux/lockdep_types.h
>> @@ -108,6 +108,10 @@ struct lock_class {
>>   	 */
>>   	struct list_head		locks_after, locks_before;
>>   
>> +	/*
>> +	 * All the fields that require re-initialization after being zapped
>> +	 * must be put after "key".
>> +	 */
>>   	const struct lockdep_subclass_key *key;
>>   	unsigned int			subclass;
>>   	unsigned int			dep_gen_id;
>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
>> index d4252b5c9863..77bbe557d48b 100644
>> --- a/kernel/locking/lockdep.c
>> +++ b/kernel/locking/lockdep.c
>> @@ -6015,10 +6015,10 @@ static void reinit_class(struct lock_class *class)
>>   	WARN_ON_ONCE(!class->lock_entry.next);
>>   	WARN_ON_ONCE(!list_empty(&class->locks_after));
>>   	WARN_ON_ONCE(!list_empty(&class->locks_before));
>> +	BUILD_BUG_ON(offsetof(struct lock_class, lock_entry) > offset);
>> +	BUILD_BUG_ON(offsetof(struct lock_class, locks_after) > offset);
>> +	BUILD_BUG_ON(offsetof(struct lock_class, locks_before) > offset);
>>   	memset(p + offset, 0, sizeof(*class) - offset);
>> -	WARN_ON_ONCE(!class->lock_entry.next);
>> -	WARN_ON_ONCE(!list_empty(&class->locks_after));
>> -	WARN_ON_ONCE(!list_empty(&class->locks_before));
>>   }
>>   
>>   static inline int within(const void *addr, void *start, unsigned long size)
>> -- 
>> 2.27.0
>>
> Yeah, except that this doesn't build because it conflicts with a
> previous patch you actually Acked:
>
>   https://lore.kernel.org/all/20211213132618.105737-1-xiujianfeng@huawei.com/T/#m0e9474a9204ec29fb2135135ce3134640a3f27b5
>
Sorry, my bad. I forgot to check tip.

I have just sent out a v2 that will work on tip.

Cheers,
Longman