[PATCH 16/33] dmaengine: at_hdmac: Fix concurrency over the active list

Tudor Ambarus
2022-08-20T12:59:33Z

The tasklet did not held the channel lock when retrieving the first active
descriptor, causing concurrency problems if issue_pending() was called in
between. If issue_pending() was called exactly after the lock was released
in the tasklet, atc_chain_complete() could complete a descriptor for which
the controller has not yet raised an interrupt.

Fixes: dc78baa2b90b ("dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller")
Reported-by: Peter Rosin <peda@axentia.se>
Cc: stable@vger.kernel.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/lkml/13c6c9a2-6db5-c3bf-349b-4c127ad3496a@axentia.se/
---
drivers/dma/at_hdmac.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index c2b3d7b63920..635c3be74399 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -897,8 +897,6 @@ atc_chain_complete(struct at_dma_chan *atchan, struct at_desc *desc)
if (!atc_chan_is_cyclic(atchan))
dma_cookie_complete(txd);

- /* Remove transfer node from the active list. */
- list_del_init(&desc->desc_node);
spin_unlock_irqrestore(&atchan->lock, flags);

dma_descriptor_unmap(txd);
@@ -930,6 +928,7 @@ atc_chain_complete(struct at_dma_chan *atchan, struct at_desc *desc)
*/
static void atc_advance_work(struct at_dma_chan *atchan)
{
+ struct at_desc *desc;
unsigned long flags;

dev_vdbg(chan2dev(&atchan->dma_chan), "advance_work\n");
@@ -937,9 +936,12 @@ static void atc_advance_work(struct at_dma_chan *atchan)
spin_lock_irqsave(&atchan->lock, flags);
if (atc_chan_is_enabled(atchan) || list_empty(&atchan->active_list))
return spin_unlock_irqrestore(&atchan->lock, flags);
- spin_unlock_irqrestore(&atchan->lock, flags);

- atc_chain_complete(atchan, atc_first_active(atchan));
+ desc = atc_first_active(atchan);
+ /* Remove the transfer node from the active list. */
+ list_del_init(&desc->desc_node);
+ spin_unlock_irqrestore(&atchan->lock, flags);
+ atc_chain_complete(atchan, desc);

/* advance work */
spin_lock_irqsave(&atchan->lock, flags);
--
2.25.1