D31002.id91681.diff
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D31002.id91681.diff
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	diff --git a/sys/dev/nvme/nvme_qpair.c b/sys/dev/nvme/nvme_qpair.c
	--- a/sys/dev/nvme/nvme_qpair.c
	+++ b/sys/dev/nvme/nvme_qpair.c
	@@ -583,13 +583,30 @@
	}

	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 cid fields 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
	+ * the phase must be the same the second time. We have to sync
	+ * before reading to ensure any bouncing completes.
	+ */
	+ status = le16toh(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(
	+ NVME_STATUS_GET_P(status) == NVME_STATUS_GET_P(cpl.status),
	+ ("Phase unexpectedly inconsistent"));

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