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Date:   Mon, 26 Jun 2023 18:25:56 +0900
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Subject: Re: [PATCH v2 1/2] seqlock: Do the lockdep annotation before locking
 in do_write_seqcount_begin_nested()
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To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        "Luis Claudio R. Goncalves" <lgoncalv@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        John Ogness <john.ogness@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Petr Mladek <pmladek@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Waiman Long <longman@redhat.com>, Will Deacon <will@kernel.org>
References: <20230623171232.892937-1-bigeasy@linutronix.de>
 <20230623171232.892937-2-bigeasy@linutronix.de>
 <d9b7c170-ed0d-5d37-e099-20d233115943@I-love.SAKURA.ne.jp>
 <20230626081254.XmorFrhs@linutronix.de>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
In-Reply-To: <20230626081254.XmorFrhs@linutronix.de>
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On 2023/06/26 17:12, Sebastian Andrzej Siewior wrote:
> On 2023-06-24 15:54:12 [+0900], Tetsuo Handa wrote:
>> Why not to do the same on the end side?
>>
>>  static inline void do_write_seqcount_end(seqcount_t *s)
>>  {
>> - 	seqcount_release(&s->dep_map, _RET_IP_);
>>  	do_raw_write_seqcount_end(s);
>> +	seqcount_release(&s->dep_map, _RET_IP_);
>>  }
> 
> I don't have a compelling argument for doing it. It is probably better
> to release the lock from lockdep's point of view and then really release
> it (so it can't be acquired before it is released).

We must do it because this is a source of possible printk() deadlock.
Otherwise, I will nack on PATCH 2/2.

> 
> Looking at other locking primitives (spin_lock_unlock(),
> mutex_unlock(),…) that is what they do in the unlock path: lockdep
> annotation followed by the actual operation. Therefore I would keep the
> current ordering to remain in-sync with the other primitives.