[PATCH] dma-mapping: don't trace the DMA address when the allocation fails

[Donggeun Yoo]

dma_alloc_attrs() passes *dma_handle to trace_dma_alloc() and
debug_dma_alloc_coherent() without checking whether the allocation
succeeded. No backend writes it on failure: dma_direct_alloc(),
iommu_dma_alloc() and the dma_map_ops instances assign it only on the
path that returns a buffer. Callers usually pass an uninitialized
automatic variable, so with the tracepoint enabled a failed allocation
records whatever the stack held, next to the virt_addr=(null) that marks
the record as an error.

The device coherent pool path is the same: a non-zero return from
dma_alloc_from_dev_coherent() means the request was handled, not that it
succeeded, so cpu_addr is NULL and dma_handle untouched once the pool
runs out.

Split both sites on cpu_addr, as dma_alloc_pages() and
dma_alloc_noncontiguous() do further down the file, and pass 0 for the
failure case like the two error paths already in this function.

Fixes: 038eb433dc14 ("dma-mapping: add tracing for dma-mapping API calls")
Fixes: 68b6dbf1f441 ("dma-mapping: trace more error paths")
Signed-off-by: Donggeun Yoo <donggeunyoo.kernel@xxxxxxxxx>
---
Compile-tested only, with CONFIG_DMA_API_DEBUG=y and CONFIG_TRACEPOINTS=y
so that both changed calls are built. The claim that no backend writes
*dma_handle on failure was checked against dma_direct_alloc() and its
helpers, iommu_dma_alloc(), iommu_dma_alloc_remap() and every in-tree
dma_map_ops .alloc implementation.

 kernel/dma/mapping.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index bf2651a70b7c..098cd57e1157 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -656,8 +656,12 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		attrs |= __DMA_ATTR_ALLOC_CC_SHARED;
 
 	if (dma_alloc_from_dev_coherent(dev, size, dma_handle, &cpu_addr)) {
-		trace_dma_alloc(dev, cpu_addr, *dma_handle, size,
-				DMA_BIDIRECTIONAL, flag, attrs);
+		if (cpu_addr)
+			trace_dma_alloc(dev, cpu_addr, *dma_handle, size,
+					DMA_BIDIRECTIONAL, flag, attrs);
+		else
+			trace_dma_alloc(dev, NULL, 0, size, DMA_BIDIRECTIONAL,
+					flag, attrs);
 		return cpu_addr;
 	}
 
@@ -676,9 +680,15 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
 		return NULL;
 	}
 
-	trace_dma_alloc(dev, cpu_addr, *dma_handle, size, DMA_BIDIRECTIONAL,
-			flag, attrs);
-	debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr, attrs);
+	if (cpu_addr) {
+		trace_dma_alloc(dev, cpu_addr, *dma_handle, size,
+				DMA_BIDIRECTIONAL, flag, attrs);
+		debug_dma_alloc_coherent(dev, size, *dma_handle, cpu_addr,
+					 attrs);
+	} else {
+		trace_dma_alloc(dev, NULL, 0, size, DMA_BIDIRECTIONAL, flag,
+				attrs);
+	}
 	return cpu_addr;
 }
 EXPORT_SYMBOL(dma_alloc_attrs);
-- 
2.53.0