[lttng-dev] [RFC] re-document rculfstack and even rename it

Lai Jiangshan laijs at cn.fujitsu.com
Thu Oct 11 22:25:40 EDT 2012

On 10/12/2012 02:22 AM, Mathieu Desnoyers wrote:
> * Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
>> rculfstack is not really require RCU-only.
>> 1) cds_lfs_push_rcu() don't need any lock, don't need RCU nor other locks.
> Good point ! I even documented this peculiarness in the
> comment at the top of _cds_lfs_push_rcu().
>> 2) cds_lfs_pop_rcu() don't only one of the following synchronization(not only RCU):
>> 	A) use rcu_read_lock() to protect cds_lfs_pop_rcu() and use synchronize_rcu()
>>            or call_rcu() to free the popped node. (current comments said we need this
>>            synchronization, and thus we named this struct with rcu prefix. But actually,
>> 	   the followings are OK, and are more popular/friendly)
>> 	B) use mutexs/locks to protect cds_lfs_pop_rcu(), we can free to free/modify the
>> 	   popped node any time, we don't need any synchronization when free them.
>> 	C) only ONE thread can call cds_lfs_pop_rcu(). (multi-providers-single customer)
>> 	D) others, like read-write locks.
>> I consider B) and C) are more popular. In linux kernel,
>> kernel/task_work.c uses a hybird ways of B) and C).
>> I suggest to rename it, Or document B) and C) at least.
> Yes, agreed! Do you suggest we introduce a "lfstack", and slowly
> deprecate rculfstack ?
> We could then document the various ways to protect "pop", and also
> implement a "splice" operation while we are there.



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