Messages in this thread | | | Date | Fri, 22 May 2015 22:18:43 +0530 | Subject | Re: [PATCH] NVMe: Avoid interrupt disable during queue init. | From | Parav Pandit <> |
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On Fri, May 22, 2015 at 9:53 PM, Keith Busch <keith.busch@intel.com> wrote: > On Fri, 22 May 2015, Parav Pandit wrote: >> >> During normal positive path probe, >> (a) device is added to dev_list in nvme_dev_start() >> (b) nvme_kthread got created, which will eventually refers to >> dev->queues[qid] to check for NULL. >> (c) dev_start() worker thread has started probing device and creating >> the queue using nvme_alloc_queue >> This is is assigning the dev->queue[qid] new pointer. >> If this is done out of order, nvme_kthread will pickup uninitialized >> q_lock, cq_phase, q_db. > > > 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(). So I was inclined towards more preferred method of rcu.
>> Other thoughts to not create nvme_kthread until all the queues are active. > > > No good, we want to poll during queue creation to detect controller > errors and broken interrupts.
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