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

[Paul E. McKenney]

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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