[lttng-dev] [PATCH liburcu] Fix lifetime of rcu_barrier()'s completion structure

Keir Fraser keir at cohodata.com
Sun Apr 20 01:35:46 EDT 2014

Mathieu Desnoyers wrote:
> ----- Original Message -----
>> From: "Keir Fraser"<keir at cohodata.com>
>> To: lttng-dev at lists.lttng.org
>> Cc: "Mathieu Desnoyers"<mathieu.desnoyers at efficios.com>, "Paul E. McKenney"<paulmck at linux.vnet.ibm.com>
>> Sent: Friday, April 18, 2014 4:12:49 PM
>> Subject: [PATCH liburcu] Fix lifetime of rcu_barrier()'s completion structure
>> [Another attachment, I must sort out to integrate with git send-mail]
>> rcu_barrier() can return as soon as completion.barrier_count==0, which
>> frees the completion struct along with the rest of its stack frame. But
>> its call_rcu callbacks may yet try to read and write completion.futex
>> via the wake_up function.
>> Fix this by calloc()ing the completion struct and implementing a
>> reference count to determine when it is eventually free()d.
>> This also fixes bug #787, since calloc() initialises all fields of the
>> structure to zero.
> I slightly edited your patch to use urcu_ref() and uatomic_sub_return()
> (simple style fix). Please let me know if you are OK with the attached
> patch.

Yes that's better, in particular I don't know how I missed the existence 
of uatomic_sub_return(). Very happy with that, thanks.

  -- Keir

> Thanks!
> Mathieu

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