linux-kernel - Re: [RFC PATCH] rcu: introduce kfree

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Date:	Thu, 18 Sep 2008 10:15:42 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>, manfred@...orfullife.com
Subject: Re: [RFC PATCH] rcu: introduce kfree_rcu()

On Thu, Sep 18, 2008 at 04:59:33PM +0800, Lai Jiangshan wrote:

[ . . . ]

> 1) unloadable modules:
>    A) use my_struct_release_rcu():
>       when we unload this modules, we need call rcu_barrier() to wait
>       all my_struct_release_rcu() had called.
>    B) use kfree_rcu():
>       if all trivial callback are removed and kfree_rcu() are used instead,
>       we do not need to wait anything. just quick finish unloading.

OK, so the trick is that the module -never- uses call_rcu()
directly, instead using -only- kfree_rcu(), along perhaps also with
synchronize_rcu().  Because kfree_rcu() does not reference module text,
you then don't need to wait at all.  Good point!

							Thanx, Paul
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