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From: Jens Axboe <axboe@kernel.dk>
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
Subject: Re: [PATCH v2 5/6] block: nr_sects_write(): Disable preemption on seqcount write
Date: Thu, 4 Jun 2020 21:22:53 -0600
Message-ID: <b8440471-e78d-8112-2ab3-c2a948095fa8@kernel.dk> (raw)
In-Reply-To: <20200603144949.1122421-6-a.darwish@linutronix.de>

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


  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-03 14:49 [PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes Ahmed S. Darwish
2020-06-03 14:49 ` [PATCH v2 5/6] block: nr_sects_write(): Disable preemption on seqcount write Ahmed S. Darwish
2020-06-05  3:22   ` Jens Axboe [this message]
2020-06-04  7:28 ` [PATCH v2 0/6] seqlock: seqcount_t call sites bugfixes Daniel Vetter
2020-06-04  8:41   ` Ahmed S. Darwish
2020-06-04 22:50 ` David Miller

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