From: Frederic Weisbecker <frederic@kernel.org>
To: Ingo Molnar <mingo@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: Tue, 12 Nov 2019 00:17:06 +0100 [thread overview]
Message-ID: <20191111231705.GC27917@lenoir> (raw)
In-Reply-To: <20191111072005.GA112047@gmail.com>
On Mon, Nov 11, 2019 at 08:20:05AM +0100, Ingo Molnar wrote:
>
> * 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?
Well, I wanted to make sure the nohz kcpustat patches are safe and I had
a last minute doubt about that irq work scenario. So I would say code
review :)
next prev parent reply other threads:[~2019-11-11 23:17 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
2019-11-11 23:17 ` Frederic Weisbecker [this message]
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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