From: Oleg Nesterov <oleg@tv-sign.ru>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@osdl.org>, Jens Axboe <jens.axboe@oracle.com>,
Alan Stern <stern@rowland.harvard.edu>,
Josh Triplett <josh@freedesktop.org>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC, PATCH 1/2] qrcu: "quick" srcu implementation
Date: Thu, 30 Nov 2006 06:37:57 +0300 [thread overview]
Message-ID: <20061130033757.GA4110@oleg> (raw)
In-Reply-To: <20061130032252.GA4101@oleg>
On 11/30, Oleg Nesterov wrote:
>
> On 11/29, Paul E. McKenney wrote:
> >
> > Hmmm... Now I am wondering if the memory barriers inherent in the
> > __wait_event() suffice for this last barrier... :-/ Thoughts?
> >
> > > + smp_mb();
>
> Fastpath skips __wait_event(), and it is possible that the reader does
> lock/unlock between the first 'mb()' and 'if (atomic_read() == 1)'.
In fact, a slow path needs (I think) it too. We can have an unrelated
wakeup, and then the reader does unlock() before we check !atomic_read()
in the __wait_event()'s loop. The reader removes us from ->wq, in that
case finish_wait() does nothing.
Oleg.
next prev parent reply other threads:[~2006-11-30 3:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-11-29 23:53 [RFC, PATCH 1/2] qrcu: "quick" srcu implementation Oleg Nesterov
2006-11-30 1:57 ` Oleg Nesterov
2006-11-30 2:46 ` Paul E. McKenney
2006-11-30 3:22 ` Oleg Nesterov
2006-11-30 3:37 ` Oleg Nesterov [this message]
2006-11-30 17:05 ` Paul E. McKenney
2006-12-01 0:14 ` Oleg Nesterov
2006-12-07 17:16 ` Paul E. McKenney
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