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From:   Waiman Long <llong@redhat.com>
Subject: Re: [PATCH v2] lockdep: Let lock_is_held_type() detect recursive read
 as read
To:     Boqun Feng <boqun.feng@gmail.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     Waiman Long <llong@redhat.com>, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20210901162255.u2vhecaxgjsjfdtc@linutronix.de>
 <9af2b074-9fcf-5aea-f37d-9b2482146489@redhat.com>
 <20210903084001.lblecrvz4esl4mrr@linutronix.de>
 <YTgc8xXuVlpOhoUT@boqun-archlinux>
Message-ID: <959eddbd-799b-3b10-0f30-0209f883d5ed@redhat.com>
Date:   Wed, 8 Sep 2021 10:40:14 -0400
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On 9/7/21 10:16 PM, Boqun Feng wrote:
> On Fri, Sep 03, 2021 at 10:40:01AM +0200, Sebastian Andrzej Siewior wrote:
>> lock_is_held_type(, 1) detects acquired read locks. It only recognized
>> locks acquired with lock_acquire_shared(). Read locks acquired with
>> lock_acquire_shared_recursive() are not recognized because a `2' is
>> stored as the read value.
>>
>> Rework the check to additionally recognise lock's read value one and two
>> as a read held lock.
>>
>> Fixes: e918188611f07 ("locking: More accurate annotations for read_lock()")
>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> ---
>> v1…v2:
>>    - simplify the read check to !!read as suggested by Waiman Long.
>>
>>   kernel/locking/lockdep.c |    2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> --- a/kernel/locking/lockdep.c
>> +++ b/kernel/locking/lockdep.c
>> @@ -5366,7 +5366,7 @@ int __lock_is_held(const struct lockdep_
>>   		struct held_lock *hlock = curr->held_locks + i;
>>   
>>   		if (match_held_lock(hlock, lock)) {
>> -			if (read == -1 || hlock->read == read)
>> +			if (read == -1 || hlock->read == !!read)
> I think this should be:
>
> 	!!hlock->read == read
>
> With that,
>
> Acked-by: Boqun Feng <boqun.feng@gmail.com>
>
You are right. It should be the other way around. read can only be -1, 
0, 1 while hlock->read can be 0, 1, 2.

Cheers,
Longman