[ltt-dev] [PATCH 0/3] Fixes for threads that are readers and writers, and lock-free queue example

[Paolo Bonzini]

On 03/01/2010 09:42 PM, Mathieu Desnoyers wrote:
> * Paolo Bonzini (pbonzini at redhat.com) wrote:
>> On 03/01/2010 09:14 PM, Mathieu Desnoyers wrote:
>>> These unpaired lock/unlock are causing this problem.
>>
>> Uh-oh.  True.
>>
>> However, the fact that a thread cannot be unregistered and then
>> reregistered remains, no?
>
> I fail to see the problem here ? Can you be more specific ?

This sequence fails:

     rcu_register_thread();
     ... some critical sections and grace periods here ...
     rcu_unregister_thread();

     ... nothing uses RCU here...

     rcu_register_thread(); // assertion failure on rcu_reader.ctr == 0

Is this also explicitly prohibited?  My patch happens to fix this too. 
(Of course there's no need to introduce _rcu_thread_{on,off}line, a one 
liner is enough).

Paolo