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Date:   Tue, 30 Jun 2020 09:11:59 +0200
From:   Daniel Wagner <dwagner@suse.de>
To:     "Ahmed S. Darwish" <a.darwish@linutronix.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        "Sebastian A. Siewior" <bigeasy@linutronix.de>,
        Steven Rostedt <rostedt@goodmis.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org
Subject: Re: [PATCH v3 16/20] iocost: Use sequence counter with associated
 spinlock
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References: <20200519214547.352050-1-a.darwish@linutronix.de>
 <20200630054452.3675847-1-a.darwish@linutronix.de>
 <20200630054452.3675847-17-a.darwish@linutronix.de>
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On Tue, Jun 30, 2020 at 07:44:48AM +0200, Ahmed S. Darwish wrote:
> A sequence counter write side critical section must be protected by some
> form of locking to serialize writers. A plain seqcount_t does not
> contain the information of which lock must be held when entering a write
> side critical section.
> 
> Use the new seqcount_spinlock_t data type, which allows to associate a
> spinlock with the sequence counter. This enables lockdep to verify that
> the spinlock used for writer serialization is held when the write side
> critical section is entered.
> 
> If lockdep is disabled this lock association is compiled out and has
> neither storage size nor runtime overhead.
> 
> Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>

Reviewed-by: Daniel Wagner <dwagner@suse.de>