LinuxKPI: expand dma_sync_single_for_cpu() in lkpi_dma_unmap()

In case lkpi_dma_unmap() would call dma_sync_single_for_cpu() we get
into a lock recursion which will trigger a panic with debug kernels.

It would be hard to provide an internal "locked" version for
dma_sync_single_for_cpu().  In the old days this would not have
been a problem but (long before we added the missing sync calls)
some locks got folded into one in a6619e8d9c1a3.

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Observed with:	iwlwifi mld
Reviewed by:	dumbbell
Differential Revision:	https://reviews.freebsd.org/D54841

1 files changed, 19 insertions, 2 deletions

diff --git a/sys/compat/linuxkpi/common/src/linux_pci.c b/sys/compat/linuxkpi/common/src/linux_pci.c
index 9e4fad45433a..612a2cb5f46b 100644
--- a/sys/compat/linuxkpi/common/src/linux_pci.c
+++ b/sys/compat/linuxkpi/common/src/linux_pci.c
@@ -1720,9 +1720,26 @@ lkpi_dma_unmap(struct device *dev, dma_addr_t dma_addr, size_t len,
 	}
 	LINUX_DMA_PCTRIE_REMOVE(&priv->ptree, dma_addr);
 
-	if ((attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
-		dma_sync_single_for_cpu(dev, dma_addr, len, direction);
+	if ((attrs & DMA_ATTR_SKIP_CPU_SYNC) != 0)
+		goto skip_sync;
 
+	/* dma_sync_single_for_cpu() unrolled to avoid lock recursicn. */
+	switch (direction) {
+	case DMA_BIDIRECTIONAL:
+		bus_dmamap_sync(obj->dmat, obj->dmamap, BUS_DMASYNC_POSTREAD);
+		bus_dmamap_sync(obj->dmat, obj->dmamap, BUS_DMASYNC_PREREAD);
+		break;
+	case DMA_TO_DEVICE:
+		bus_dmamap_sync(obj->dmat, obj->dmamap, BUS_DMASYNC_POSTWRITE);
+		break;
+	case DMA_FROM_DEVICE:
+		bus_dmamap_sync(obj->dmat, obj->dmamap, BUS_DMASYNC_POSTREAD);
+		break;
+	default:
+		break;
+	}
+
+skip_sync:
 	bus_dmamap_unload(obj->dmat, obj->dmamap);
 	bus_dmamap_destroy(obj->dmat, obj->dmamap);
 	DMA_PRIV_UNLOCK(priv);