Re: [PATCH] cred - synchronize rcu before releasing cred

From: Paul E. McKenney
Date: Thu Jul 29 2010 - 02:06:32 EST

On Wed, Jul 28, 2010 at 01:47:06PM +0100, David Howells wrote:
> David Howells <dhowells@xxxxxxxxxx> wrote:
> > Yeah. I think there are three alternatives:
> There's a fourth alternative too:
> (4) I could try and make it so that if the RCU cleanup routine sees it with a
> non-zero usage count, then it just ignores it. This, however, would
> require call_rcu() to be able to cope with requeueing.

It is perfectly legal for an RCU callback to invoke call_rcu(). However,
this should be used -only- to wait for RCU readers. If there are no
RCU readers, the callback might be re-invoked in very short order,
expecially on UP systems.

Or am I misunderstanding what you mean by "require call_rcu() to be
able to cope iwth requeueing"?

Thanx, Paul
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