linux-kernel - Re: [PATCH] Markers : fix reentrancy

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Date:	Tue, 30 Sep 2008 11:52:45 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: [PATCH] Markers : fix reentrancy

* Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca> wrote:
> 
> > Lai Jiangshan <laijs@...fujitsu.com> wrote :
> > > marker_synchronize_unregister must be called _also_ between unregistration
> > > and destruction the data that unregistration-ed probes need to make sure
> > > there is no caller executing a probe when it's data is destroyed.
> > > 
> > 
> > Ah, you're right. I looked again through your patch description and I
> > think using a :
> > 
> > 
> > if (entry->rcu_pending)
> >                 rcu_barrier_sched();
> > 
> > After each time the markers_mutex is taken would keep the fast batch 
> > registration/unregistration and fix the reentrancy problem. The 
> > following patch should address the problem.
> 
> could you please send a delta patch against tip/master? Lai's patch is 
> already applied and is tested. Thanks,
> 
> 	Ingo

Hrm,

Most of Lai "simplifications" to use synchronize_sched() instead of
call_rcu_sched() will make batch registration/unregistration much
slower (very noticeable on ~50 markers on a loaded machine). It also
contains two different fixes in one, one of which has been nacked.

The correct list of changes against tip now becomes :

Revert commit d587284c1d26b796bf52a6e3d3f783db4e462119
Apply patch "Markers : marker_synchronize_unregister()"
Apply patch "Markers : probe example fix teardown"
Apply patch "Markers : documentation fix teardown"
Apply patch "sputrace : use marker_synchronize_unregister()"
Apply patch "Markers : fix reentrancy"

Sorry, but rebasing those marker fixes will just make all those changes
really messy. I think the cleanest way is to just revert. :-/

Mathieu
-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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