linux-kernel - Re: [PATCH RFC tip/core/rcu 23/23] vhost: add _

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Message-ID: <20100517203349.GA14994@redhat.com>
Date:	Mon, 17 May 2010 23:33:49 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, Arnd Bergmann <arnd@...ay.de.ibm.com>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH RFC tip/core/rcu 23/23] vhost: add __rcu annotations

On Thu, May 13, 2010 at 08:23:40AM -0700, Paul E. McKenney wrote:
> On Thu, May 13, 2010 at 03:07:23PM +0200, Peter Zijlstra wrote:
> > On Wed, 2010-05-12 at 16:00 -0700, Paul E. McKenney wrote:
> > > Any thoughts?  One approach would be to create a separate lockdep class
> > > for vhost workqueue state, similar to the approach used in instrument
> > > rcu_read_lock() and friends. 
> > 
> > workqueue_struct::lockdep_map, its held while executing worklets.
> > 
> > lock_is_held(&vhost_workqueue->lockdep_map), should do as you want.
> 
> Thank you, Peter!!!
> 
> 							Thanx, Paul

vhost in fact does flush_work rather than
flush_workqueue, so while for now everything runs
from vhost_workqueue in theory nothing would break
if we use some other workqueue or even a combination
thereof.

I guess when/if this happens, we could start by converting
to _raw and then devise a solution.

By the way what would be really nice is if we had a way
to trap when rcu protected pointer is freed without a flush
while some reader is running. Current annotation does not
allow this, does it?

-- 
MST
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