D31002.id91674.diff
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D31002.id91674.diff
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	Index: sys/dev/nvme/nvme_qpair.c
	===================================================================
	--- sys/dev/nvme/nvme_qpair.c
	+++ sys/dev/nvme/nvme_qpair.c
	@@ -583,13 +583,28 @@
	}

	while (1) {
	- cpl = qpair->cpl[qpair->cq_head];
	+ uint16_t status;

	- /* Convert to host endian */
	+ /*
	+ * We need to do this dance to avoid a race between the host and
	+ * the device where the device overtakes the host while the host
	+ * is reading this record, leaving the status field 'new' and the
	+ * sqhd and sqid potentially stale. If the phase doesn't match,
	+ * that means status hasn't yet been updated and we'll get any
	+ * pending changes next time. It also means that it must be the
	+ * same the second time. We have to sync before reading to ensure
	+ * any bouncing completes.
	+ */
	+ status = le16toh(atomic_load_acq_16(&qpair->cpl[qpair->cq_head].status));
	+ if (NVME_STATUS_GET_P(status) != qpair->phase)
	+ break;
	+
	+ bus_dmamap_sync(qpair->dma_tag, qpair->queuemem_map,
	+ BUS_DMASYNC_POSTREAD \| BUS_DMASYNC_POSTWRITE);
	+ cpl = qpair->cpl[qpair->cq_head];
	nvme_completion_swapbytes(&cpl);

	- if (NVME_STATUS_GET_P(cpl.status) != qpair->phase)
	- break;
	+ KASSERT(status == cpl.status, ("received completion for unknown cmd"));

	tr = qpair->act_tr[cpl.cid];