[PATCH v3 05/12] dmaengine: at_xdmac: Fix race for the tx desc callback

[Tudor Ambarus]

The transfer descriptors were wrongly moved to the free descriptors list
before calling the tx desc callback. As the DMA engine drivers drop any
locks before calling the callback function, txd could be taken again,
resulting in its callback called prematurely. Fix the race for the tx desc
callback by moving the xfer desc into the free desc list after the
callback is invoked.

Fixes: e1f7c9eee707 ("dmaengine: at_xdmac: creation of the atmel eXtended DMA Controller driver")
Signed-off-by: Tudor Ambarus <tudor.ambarus at microchip.com>
---
 drivers/dma/at_xdmac.c | 25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index 83c031207530..d5b37459f906 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -1582,20 +1582,6 @@ at_xdmac_tx_status(struct dma_chan *chan, dma_cookie_t cookie,
 	return ret;
 }
 
-/* Call must be protected by lock. */
-static void at_xdmac_remove_xfer(struct at_xdmac_chan *atchan,
-				    struct at_xdmac_desc *desc)
-{
-	dev_dbg(chan2dev(&atchan->chan), "%s: desc 0x%p\n", __func__, desc);
-
-	/*
-	 * Remove the transfer from the transfer list then move the transfer
-	 * descriptors into the free descriptors list.
-	 */
-	list_del(&desc->xfer_node);
-	list_splice_init(&desc->descs_list, &atchan->free_descs_list);
-}
-
 static void at_xdmac_advance_work(struct at_xdmac_chan *atchan)
 {
 	struct at_xdmac_desc	*desc;
@@ -1704,7 +1690,8 @@ static void at_xdmac_tasklet(struct tasklet_struct *t)
 
 		txd = &desc->tx_dma_desc;
 		dma_cookie_complete(txd);
-		at_xdmac_remove_xfer(atchan, desc);
+		/* Remove the transfer from the transfer list. */
+		list_del(&desc->xfer_node);
 		spin_unlock_irq(&atchan->lock);
 
 		if (txd->flags & DMA_PREP_INTERRUPT)
@@ -1713,6 +1700,8 @@ static void at_xdmac_tasklet(struct tasklet_struct *t)
 		dma_run_dependencies(txd);
 
 		spin_lock_irq(&atchan->lock);
+		/* Move the xfer descriptors into the free descriptors list. */
+		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
 		at_xdmac_advance_work(atchan);
 		spin_unlock_irq(&atchan->lock);
 	}
@@ -1859,8 +1848,10 @@ static int at_xdmac_device_terminate_all(struct dma_chan *chan)
 		cpu_relax();
 
 	/* Cancel all pending transfers. */
-	list_for_each_entry_safe(desc, _desc, &atchan->xfers_list, xfer_node)
-		at_xdmac_remove_xfer(atchan, desc);
+	list_for_each_entry_safe(desc, _desc, &atchan->xfers_list, xfer_node) {
+		list_del(&desc->xfer_node);
+		list_splice_init(&desc->descs_list, &atchan->free_descs_list);
+	}
 
 	clear_bit(AT_XDMAC_CHAN_IS_PAUSED, &atchan->status);
 	clear_bit(AT_XDMAC_CHAN_IS_CYCLIC, &atchan->status);
-- 
2.25.1