swiotlb: remove panic for alloc_coherent failure

swiotlb_alloc_coherent calls panic() when allocated swiotlb pages is
not fit for a device's dma mask. However, alloc_coherent failure is
not a disaster at all. AFAIK, none of other x86 and IA64 IOMMU
implementations don't crash in case of alloc_coherent failure.

There are some drivers that don't check alloc_coherent failure but not
many (about ten and I've already started to fix some of
them). alloc_coherent returns NULL in case of failure so it's likely
that these guilty drivers crash immediately. So swiotlb doesn't need
to call panic() just for them.
Reported-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Tested-by: NTakashi Iwai <tiwai@suse.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

lib/swiotlb.c

@@ -497,8 +497,10 @@ swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 		printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
 		       (unsigned long long)*hwdev->dma_mask,
 		       (unsigned long long)dev_addr);
-		panic("swiotlb_alloc_coherent: allocated memory is out of "
-		      "range for device");
+
+		/* DMA_TO_DEVICE to avoid memcpy in unmap_single */
+		unmap_single(hwdev, ret, size, DMA_TO_DEVICE);
+		return NULL;
 	}
 	*dma_handle = dev_addr;
 	return ret;