On Wed, Mar 02, 2016 at 09:08:31PM +0800, Jianyu Zhan wrote:
...
> 3) READ_ONCE() _might_ prevent more _theoretical_ "optimizations" by the
> compiler:
>
> The above retry logic is effectively the same as:
>
> while (lock_ptr = READ_ONCE(q->lock_ptr)) {
> spin_lock(lock_ptr)
The spin_lock() is memory barrier, and therefor a general compiler barrier. The
READ_ONCE would be redundant in this case.
Unless you can demonstrate a failure mode in disassembly, or can point out how
the spin_lock barrier is insufficient that I have missed, this third point is
already covered.
--
Darren Hart
Intel Open Source Technology Center
