Messages in this thread | | | From | David Howells <> | Subject | Re: [PATCH] cred - synchronize rcu before releasing cred | Date | Thu, 29 Jul 2010 09:34:20 +0100 |
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Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> 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"?
I mean for call_rcu() to be called on an object that's already been call_rcu()'d but not yet processed.
For example if struct cred gets its usage count reduced to 0, __put_cred() will call_rcu() it, but what happens if someone comes along and resurrects it by increasing its usage count again? And what happens if the usage count is reduced back to zero and __put_cred() calls call_rcu() again before put_cred_rcu() has a chance to run?
David
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