[PATCH] dma: fix call order in dmam_free_coherent

[PATCH] dma: fix call order in dmam_free_coherent

[Lance Richardson]

dmam_free_coherent() frees a DMA allocation, which makes the
freed vaddr available for reuse, then calls devres_destroy()
to remove and free the data structure used to track the DMA
allocation. Between the two calls, it is possible for a
concurrent task to make an allocation with the same vaddr
and add it to the devres list.

If this happens, there will be two entries in the devres list
with the same vaddr and devres_destroy() can free the wrong
entry, triggering the WARN_ON() in dmam_match.

Fix by destroying the devres entry before freeing the DMA
allocation.

Tested:
  kokonut //net/encryption
    http://sponge2/b9145fe6-0f72-4325-ac2f-a84d81075b03

Fixes: 9ac7849e35f7 ("devres: device resource management")
Signed-off-by: Lance Richardson <rlance@google.com>
---
 kernel/dma/mapping.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 98e3d873792e..0492fb58be7b 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -59,8 +59,8 @@ void dmam_free_coherent(struct device *dev, size_t size, void *vaddr,
 {
 	struct dma_devres match_data = { size, vaddr, dma_handle };
 
-	dma_free_coherent(dev, size, vaddr, dma_handle);
 	WARN_ON(devres_destroy(dev, dmam_release, dmam_match, &match_data));
+	dma_free_coherent(dev, size, vaddr, dma_handle);
 }
 EXPORT_SYMBOL(dmam_free_coherent);
 
-- 
2.45.2.993.g49e7a77208-goog

Re: [PATCH] dma: fix call order in dmam_free_coherent

[Christoph Hellwig]

Thanks, applied.