linux-kernel - Re: [PATCH] markers: fix unregister bug and reenter bug

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Message-ID: <20080929150320.GA11245@Krystal>
Date:	Mon, 29 Sep 2008 11:03:20 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] markers: fix unregister bug and reenter bug

Hi Lai,

I'll have to nack this fix :

One fix I already posted makes sure every marker unregister callers call
synchronize_sched() _at some point_ before module unload. It thus makes
sure we can do batch unregistration without doing multiple
synchronize_sched calls.

Also, there is no need to do the synchronize_sched with the marker mutex
held. call_rcu_sched takes care of making sure the previous quiescent
state is over before calling kfree. This means that when we return from
the register/unregister functions, there may still be markers "in
flight" using the old markers. Again, why would it be a problem ?

Thanks,

Mathieu

P.S. : I'll send along the patches I am referring to. Ingo, those should
probably be merged if they are not in -tip already.

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