linux-kernel - Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global reader-writer lock backend

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Message-ID: <1358888061.21576.57.camel@gandalf.local.home>
Date:	Tue, 22 Jan 2013 15:54:21 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	linux-doc@...r.kernel.org, peterz@...radead.org,
	fweisbec@...il.com, linux-kernel@...r.kernel.org, mingo@...nel.org,
	linux-arch@...r.kernel.org, linux@....linux.org.uk,
	xiaoguangrong@...ux.vnet.ibm.com, wangyun@...ux.vnet.ibm.com,
	paulmck@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	linux-pm@...r.kernel.org, rusty@...tcorp.com.au, rjw@...k.pl,
	namhyung@...nel.org, tglx@...utronix.de,
	linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
	oleg@...hat.com, sbw@....edu, tj@...nel.org,
	akpm@...ux-foundation.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v5 01/45] percpu_rwlock: Introduce the global
 reader-writer lock backend

On Wed, 2013-01-23 at 01:28 +0530, Srivatsa S. Bhat wrote:

> > I thought global locks are now fair. That is, a reader will block if a
> > writer is waiting. Hence, the above should deadlock on the current
> > rwlock_t types.
> > 
> 
> Oh is it? Last I checked, lockdep didn't complain about this ABBA scenario!

It doesn't and Peter Zijlstra said we need to fix that ;-)  It only
recently became an issue with the new "fair" locking of rwlocks.

-- Steve


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