linux-kernel - Re: [PATCH v3 16/20] iocost: Use sequence counter with associated spinlock

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Message-ID: <20200630071159.llgfzs3n4xekexcw@beryllium.lan>
Date:   Tue, 30 Jun 2020 09:11:59 +0200
From:   Daniel Wagner <dwagner@...e.de>
To:     "Ahmed S. Darwish" <a.darwish@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        "Sebastian A. Siewior" <bigeasy@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org
Subject: Re: [PATCH v3 16/20] iocost: Use sequence counter with associated
 spinlock

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@...utronix.de>

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