On Mon, Jun 19, 2017 at 9:45 AM, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > ehm. You sure? I simply delayed the lock-dropping _after_ the state > variable was been modified. So it was basically what your patch did > except it was unlocked later… Yes, I'm sure. You moved the call to invalidate_batched_entropy() to be after the assignment of crng_init. However, the call to invalidate_batched_entropy() must be made _before_ the assignment of crng_init. >> > Are use about that? I am not sure that the gcc will inline "crng_init" >> > read twice. It is not a local variable. READ_ONCE() is usually used >> > where gcc could cache a memory access but you do not want this. But hey! >> > If someone knows better I am here to learn. >> >> The whole purpose is that I _want_ it to cache the memory access so >> that it is _not_ inlined. So, based on your understanding, it does >> exactly what I intended it to do. The reason is that I'd like to avoid >> a lock imbalance, which could happen if the read is inlined. > > So it was good as it was which means you can drop that READ_ONCE(). Except READ_ONCE ensures that the compiler will never inline it, so it actually needs to stay.
