Patch "dmaengine: at_xdmac: Fix race for the tx desc callback" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    dmaengine: at_xdmac: Fix race for the tx desc callback

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dmaengine-at_xdmac-fix-race-for-the-tx-desc-callback.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 70dea6dc22938a62825d23b4a7ebbf82129e3f56
Author: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>
Date:   Wed Dec 15 13:01:08 2021 +0200

    dmaengine: at_xdmac: Fix race for the tx desc callback
    
    [ Upstream commit b63e5cb94ad6947ab5fe38b5a9417dcfd0bc6122 ]
    
    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@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20211215110115.191749-6-tudor.ambarus@xxxxxxxxxxxxx
    Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
index c6b200f0145ba..f7b0de4f4667d 100644
--- a/drivers/dma/at_xdmac.c
+++ b/drivers/dma/at_xdmac.c
@@ -1586,20 +1586,6 @@ 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;
@@ -1711,7 +1697,8 @@ 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)
@@ -1720,6 +1707,8 @@ 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);
 	}
@@ -1866,8 +1855,10 @@ 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);