dma: fix call order in dmam_free_coherent

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>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 81de84318ccc71ad1b56f707d589977882c25834..b1c18058d55f8d1ce759d6b70691c56d9073b30c 100644 (file)
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -67,8 +67,8 @@ 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);