[PATCH] NVMe: Fix possible scheduling while atomic error
Keith Busch
keith.busch at intel.com
Mon May 23 06:41:16 PDT 2016
On Mon, May 23, 2016 at 03:58:07AM -0700, Christoph Hellwig wrote:
> On Tue, May 17, 2016 at 03:37:42PM -0600, Keith Busch wrote:
> > rcu_read_lock();
> > list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
> > - queue_flag_clear_unlocked(QUEUE_FLAG_STOPPED, ns->queue);
> > + spin_lock_irq(ns->queue->queue_lock);
> > + queue_flag_clear(QUEUE_FLAG_STOPPED, ns->queue);
> > + spin_unlock_irq(ns->queue->queue_lock);
>
> What's the rationale for this change?
That was to make it so nvme_queue_rq wouldn't see a stopped flag just
before it was starting.
> > @@ -609,6 +609,12 @@ static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
> > spin_unlock_irq(&nvmeq->q_lock);
> > return BLK_MQ_RQ_QUEUE_OK;
> > out:
> > + if (ret == BLK_MQ_RQ_QUEUE_BUSY) {
> > + spin_lock_irq(ns->queue->queue_lock);
> > + if (blk_queue_stopped(req->q))
> > + blk_mq_stop_hw_queues(ns->queue);
> > + spin_unlock_irq(ns->queue->queue_lock);
>
> Shouldn't we do this where set the stopped flag on the queue instead?
It's moved out of that function holding the rcu read lock since
blk_mq_stop_hw_queues potentially sleeps.
But the above is also broken because it's holding a spinlock, so this
patch is no good.
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