From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
Ingo Molnar <mingo@redhat.com>,
linux-mm@kvack.org, Shaohua Li <shli@kernel.org>,
linux-raid@vger.kernel.org,
Anna-Maria Gleixner <anna-maria@linutronix.de>
Subject: Re: [PATCH 3/8] md: raid5: use refcount_t for reference counting instead atomic_t
Date: Wed, 23 May 2018 14:55:42 +0200 [thread overview]
Message-ID: <20180523125542.GT12198@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180523125007.pbxcxef622cde3jz@linutronix.de>
On Wed, May 23, 2018 at 02:50:07PM +0200, Sebastian Andrzej Siewior wrote:
> On 2018-05-23 14:36:15 [+0200], Peter Zijlstra wrote:
> > > Most changes are 1:1 replacements except for
> > > BUG_ON(atomic_inc_return(&sh->count) != 1);
> >
> > That doesn't look right, 'inc_return == 1' implies inc-from-zero, which
> > is not allowed by refcount.
> >
> > > which has been turned into
> > > refcount_inc(&sh->count);
> > > BUG_ON(refcount_read(&sh->count) != 1);
> >
> > And that is racy, you can have additional increments in between.
>
> so do we stay with the atomic* API here or do we extend refcount* API?
Stay with the atomic; I'll look at the rest of these patches, but raid5
looks like a usage-count, not a reference count.
I'll probably ack your initial set and parts of this.. but let me get to
the end of this first.
next prev parent reply other threads:[~2018-05-23 12:55 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-09 19:36 [PATCH v2 0/8] Introduce refcount_dec_and_lock_irqsave() Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 1/8] bdi: use refcount_t for reference counting instead atomic_t Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 2/8] userns: " Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 3/8] md: raid5: " Sebastian Andrzej Siewior
2018-05-23 12:36 ` Peter Zijlstra
2018-05-23 12:50 ` Sebastian Andrzej Siewior
2018-05-23 12:55 ` Peter Zijlstra [this message]
2018-05-23 13:21 ` Matthew Wilcox
2018-05-23 17:49 ` Peter Zijlstra
2018-05-23 19:22 ` Shaohua Li
2018-05-24 7:14 ` Peter Zijlstra
2018-05-09 19:36 ` [PATCH 4/8] locking/refcount: implement refcount_dec_and_lock_irqsave() Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 5/8] bdi: Use irqsave variant of refcount_dec_and_lock() Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 6/8] userns: " Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 7/8] md: raid5: " Sebastian Andrzej Siewior
2018-05-09 19:36 ` [PATCH 8/8] md: raid5: Do not disable irq on release_inactive_stripe_list() call Sebastian Andrzej Siewior
2018-05-23 13:01 ` [PATCH v2 0/8] Introduce refcount_dec_and_lock_irqsave() Peter Zijlstra
2018-05-23 13:09 ` Sebastian Andrzej Siewior
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