dmaengine: tegra-apb: Prevent race conditions of tasklet vs free list

The interrupt handler puts a half-completed DMA descriptor on a free list
and then schedules tasklet to process bottom half of the descriptor that
executes client's callback, this creates possibility to pick up the busy
descriptor from the free list. Thus, let's disallow descriptor's re-use
until it is fully processed.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200209163356.6439-3-digetx@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c
index 319f31d..4a750e2 100644 (file)
--- a/drivers/dma/tegra20-apb-dma.c
+++ b/drivers/dma/tegra20-apb-dma.c
@@ -281,7 +281,7 @@ static struct tegra_dma_desc *tegra_dma_desc_get(
 
        /* Do not allocate if desc are waiting for ack */
        list_for_each_entry(dma_desc, &tdc->free_dma_desc, node) {
-               if (async_tx_test_ack(&dma_desc->txd)) {
+               if (async_tx_test_ack(&dma_desc->txd) && !dma_desc->cb_count) {
                        list_del(&dma_desc->node);
                        spin_unlock_irqrestore(&tdc->lock, flags);
                        dma_desc->txd.flags = 0;