[PATCH] dmaengine: pxa: fix double counting of the hw descriptors

[Sascha Hauer]

pxad_alloc_desc() was converted from

	kzalloc(struct_size(sw_desc, hw_desc, nb_hw_desc), GFP_NOWAIT)

to kzalloc_flex(). hw_desc[] is annotated with __counted_by(nb_desc), so
__alloc_flex() now initializes sw_desc->nb_desc to nb_hw_desc itself.
The loop below it still increments nb_desc for every descriptor it
allocates though, so nb_desc ends up being twice the number of
descriptors that are actually there.

Drop the now redundant increment. The error path has to set nb_desc to
the number of descriptors allocated so far, otherwise pxad_free_desc()
would free entries that were never allocated.

Fixes: 69050f8d6d075 ("treewide: Replace kmalloc with kmalloc_obj for non-scalar types")
Assisted-by: Claude:claude-opus-5
Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
---
pxad_alloc_desc() was converted from

        kzalloc(struct_size(sw_desc, hw_desc, nb_hw_desc), GFP_NOWAIT)

to kzalloc_flex(). hw_desc[] is annotated with __counted_by(nb_desc), so
__alloc_flex() now initializes sw_desc->nb_desc to nb_hw_desc itself.
The loop below it still increments nb_desc for every descriptor it
allocates though, so nb_desc ends up being twice the number of
descriptors that are actually there.

Drop the now redundant increment. The error path has to set nb_desc to
the number of descriptors allocated so far, otherwise pxad_free_desc()
would free entries that were never allocated.
---
 drivers/dma/pxa_dma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/pxa_dma.c b/drivers/dma/pxa_dma.c
index fa2ee0b3e09f8..8252d27be8c3c 100644
--- a/drivers/dma/pxa_dma.c
+++ b/drivers/dma/pxa_dma.c
@@ -752,10 +752,11 @@ pxad_alloc_desc(struct pxad_chan *chan, unsigned int nb_hw_desc)
 			dev_err(&chan->vc.chan.dev->device,
 				"%s(): Couldn't allocate the %dth hw_desc from dma_pool %p\n",
 				__func__, i, sw_desc->desc_pool);
+			/* Only the descriptors below i have been allocated */
+			sw_desc->nb_desc = i;
 			goto err;
 		}
 
-		sw_desc->nb_desc++;
 		sw_desc->hw_desc[i] = desc;
 
 		if (i == 0)

---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260817-dmaengine-pxa-64152bb34313

Best regards,
-- 
Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>