On Wed, 8 Aug 2018 06:03:02 -0700 "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> What's wrong with a this_cpu_inc()? It's atomic for the CPU. Although > > it wont be atomic for the capture of the idx. But I also don't see > > interrupts being disabled, thus an NMI is no different than any > > interrupt doing the same thing, right? > > On architectures without increment-memory instructions, if you take an NMI > between the load from sp->sda->srcu_lock_count and the later store, you > lose a count. Note that both __srcu_read_lock() and __srcu_read_unlock() > do increments of different locations, so you cannot rely on the usual > "NMI fixes up before exit" semantics you get when incrementing and > decrementing the same location. And how is this handled in the interrupt case? Interrupts are not disabled here. I would also argue that architectures without increment-memory instructions shouldn't have NMIs ;-) -- Steve
