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Subject: Re: [PATCH v2 5/6] block: nr_sects_write(): Disable preemption on
 seqcount write
To:     "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>
Cc:     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>,
        Vivek Goyal <vgoyal@redhat.com>, linux-block@vger.kernel.org
References: <20200603144949.1122421-1-a.darwish@linutronix.de>
 <20200603144949.1122421-6-a.darwish@linutronix.de>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <b8440471-e78d-8112-2ab3-c2a948095fa8@kernel.dk>
Date:   Thu, 4 Jun 2020 21:22:53 -0600
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On 6/3/20 8:49 AM, Ahmed S. Darwish wrote:
> For optimized block readers not holding a mutex, the "number of sectors"
> 64-bit value is protected from tearing on 32-bit architectures by a
> sequence counter.
> 
> Disable preemption before entering that sequence counter's write side
> critical section. Otherwise, the read side can preempt the write side
> section and spin for the entire scheduler tick. If the reader belongs to
> a real-time scheduling class, it can spin forever and the kernel will
> livelock.

Applied, thanks.

-- 
Jens Axboe