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From: Ingo Molnar <mingo@kernel.org>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/4] irq_work: Fix irq_work_claim() ordering
Date: Mon, 11 Nov 2019 08:20:05 +0100	[thread overview]
Message-ID: <20191111072005.GA112047@gmail.com> (raw)
In-Reply-To: <20191108160858.31665-3-frederic@kernel.org>


* Frederic Weisbecker <frederic@kernel.org> wrote:

> When irq_work_claim() finds IRQ_WORK_PENDING flag already set, we just
> return and don't raise a new IPI. We expect the destination to see
> and handle our latest updades thanks to the pairing atomic_xchg()
> in irq_work_run_list().
> 
> But cmpxchg() doesn't guarantee a full memory barrier upon failure. So
> it's possible that the destination misses our latest updates.
> 
> So use atomic_fetch_or() instead that is unconditionally fully ordered
> and also performs exactly what we want here and simplify the code.

Just curious, how was this bug found - in the wild, or via code review?

Thanks,

	Ingo

  reply	other threads:[~2019-11-11  7:20 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-08 16:08 [PATCH 0/4] irq_work: Fix ordering issue Frederic Weisbecker
2019-11-08 16:08 ` [PATCH 1/4] irq_work: Convert flags to atomic_t Frederic Weisbecker
2019-11-11  8:00   ` Ingo Molnar
2019-11-11 22:56     ` Frederic Weisbecker
2019-11-11  9:32   ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2019-11-08 16:08 ` [PATCH 2/4] irq_work: Fix irq_work_claim() ordering Frederic Weisbecker
2019-11-11  7:20   ` Ingo Molnar [this message]
2019-11-11 23:17     ` Frederic Weisbecker
2019-11-11  9:32   ` [tip: irq/core] irq_work: Fix irq_work_claim() memory ordering tip-bot2 for Frederic Weisbecker
2019-11-08 16:08 ` [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing Frederic Weisbecker
2019-11-11  9:32   ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2019-11-12 20:27   ` [PATCH 3/4] " Leonard Crestez
2019-11-13  0:22     ` Frederic Weisbecker
2019-11-08 16:08 ` [RFC PATCH 4/4] irq_work: Weaken ordering in irq_work_run_list() Frederic Weisbecker
2019-11-11  8:43   ` Peter Zijlstra
2019-11-11 22:38     ` Frederic Weisbecker

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