nvme-pci: Hold cq_poll_lock while completing CQEs

Completions need to consumed in the same order the controller submitted
them, otherwise future completion entries may overwrite ones we haven't
handled yet. Hold the nvme queue's poll lock while completing new CQEs to
prevent another thread from freeing command tags for reuse out-of-order.

Fixes: dabcefa ("nvme: provide optimized poll function for separate poll queues")
Signed-off-by: Bijan Mottahedeh <[email protected]>
Reviewed-by: Sagi Grimberg <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Signed-off-by: Keith Busch <[email protected]>

Author: Bijan Mottahedeh

drivers/nvme/host/pci.c

@@ -1078,9 +1078,9 @@ static int nvme_poll(struct blk_mq_hw_ctx *hctx)
 
 	spin_lock(&nvmeq->cq_poll_lock);
 	found = nvme_process_cq(nvmeq, &start, &end, -1);
+	nvme_complete_cqes(nvmeq, start, end);
 	spin_unlock(&nvmeq->cq_poll_lock);
 
-	nvme_complete_cqes(nvmeq, start, end);
 	return found;
 }