[PATCH] dmaengine: mv_xor: return descriptor to free pool on io_win failure

[Rosen Penev <rosenp@gmail.com>]

When mv_xor_prep_dma_xor() allocates a descriptor slot and then
mv_xor_add_io_win() fails in the source-address loop, the slot
stays on the allocated list and is never reclaimed, leaking a
descriptor resource.

Return the slot to the free pool under the channel lock before
returning NULL on failure.

Fixes: 77ff7a706f01 ("mv_xor: Add support for IO (PCIe) src/dst areas")
Assisted-by: opencode:big-pickle
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/dma/mv_xor.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
index 25ed61f1b089..dd4f150d5fb1 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -583,8 +583,13 @@ mv_xor_prep_dma_xor(struct dma_chan *chan, dma_addr_t dest, dma_addr_t *src,
 		while (src_cnt--) {
 			/* Check if a new window needs to get added for 'src' */
 			ret = mv_xor_add_io_win(mv_chan, src[src_cnt]);
-			if (ret)
+			if (ret) {
+				spin_lock_bh(&mv_chan->lock);
+				list_move_tail(&sw_desc->node,
+					       &mv_chan->free_slots);
+				spin_unlock_bh(&mv_chan->lock);
 				return NULL;
+			}
 			mv_desc_set_src_addr(sw_desc, src_cnt, src[src_cnt]);
 		}
 	}
-- 
2.55.0