On Fri, May 22, 2015 at 10:37 PM, Keith Busch <keith.bu...@intel.com> wrote: > On Fri, 22 May 2015, Parav Pandit wrote: >> >> On Fri, May 22, 2015 at 9:53 PM, Keith Busch <keith.bu...@intel.com> >> wrote: >>> >>> A memory barrier before incrementing the dev->queue_count (and assigning >>> the pointer in the array before that) should address this concern. >> >> >> Sure. mb() will solve the publisher side problem. RCU is wrapper around >> mb(). >> However mb() doesn't solve the issue of q_lock variable getting >> fetched before if (!nvmeq) condition being executed, by value >> compilation optimizations in nvme_kthread(). > > > Eh? The value of dev->queue_count prevents the thread's for-loop from > iterating that nvmeq before the q_lock is initialized.
I agree to it that nvmeq won't be null after mb(); That alone is not sufficient. What I have proposed in previous email is, Converting, struct nvme_queue *nvmeq = dev->queues[i]; if (!nvmeq) continue; spin_lock_irq(nvmeq->q_lock); to replace with, struct nvme_queue *nvmeq = rcu_dereference(dev->queues[i]); if (!nvmeq) continue; spin_lock_irq(nvmeq->q_lock); This will prevent fetching content of q_lock before checking for NULL condition. Classic usage or RCU. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/