Messages in this thread | | | Date | Fri, 22 May 2015 23:03:58 +0530 | Subject | Re: [PATCH] NVMe: Avoid interrupt disable during queue init. | From | Parav Pandit <> |
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On Fri, May 22, 2015 at 10:37 PM, Keith Busch <keith.busch@intel.com> wrote: > On Fri, 22 May 2015, Parav Pandit wrote: >> >> On Fri, May 22, 2015 at 9:53 PM, Keith Busch <keith.busch@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.
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