[PATCH] dmaengine: mmp_pdma: Check virtual channel before scheduling tasklet

[Ruoyu Wang <ruoyuw560@gmail.com>]

mmp_pdma_chan_handler() clears a physical-channel interrupt and then
unconditionally schedules phy->vchan->tasklet. The physical channel can
be detached from its virtual channel when the channel is terminated or
when no pending work remains, so a late or shared interrupt can reach the
handler with phy->vchan already NULL.

Snapshot phy->vchan in the interrupt path, skip tasklet scheduling when
there is no virtual channel, and use the same snapshot for the BUSERR
warning. Use WRITE_ONCE() for the matching attach/detach stores because
the IRQ path reads this pointer without taking phy_lock.

This issue was found by a static analysis checker and confirmed by
manual source review.

Fixes: c8acd6aa6bed ("dmaengine: mmp-pdma support")
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
---
 drivers/dma/mmp_pdma.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
index 386e85cd4882a..6f379e9f10017 100644
--- a/drivers/dma/mmp_pdma.c
+++ b/drivers/dma/mmp_pdma.c
@@ -351,6 +351,7 @@ static void disable_chan(struct mmp_pdma_phy *phy)
 
 static int clear_chan_irq(struct mmp_pdma_phy *phy)
 {
+	struct mmp_pdma_chan *vchan;
 	u32 dcsr;
 	u32 dint = readl(phy->base + DINT);
 	u32 reg = (phy->idx << 2) + DCSR;
@@ -361,8 +362,9 @@ static int clear_chan_irq(struct mmp_pdma_phy *phy)
 	/* clear irq */
 	dcsr = readl(phy->base + reg);
 	writel(dcsr, phy->base + reg);
-	if ((dcsr & DCSR_BUSERR) && (phy->vchan))
-		dev_warn(phy->vchan->dev, "DCSR_BUSERR\n");
+	vchan = READ_ONCE(phy->vchan);
+	if ((dcsr & DCSR_BUSERR) && vchan)
+		dev_warn(vchan->dev, "DCSR_BUSERR\n");
 
 	return 0;
 }
@@ -370,11 +372,16 @@ static int clear_chan_irq(struct mmp_pdma_phy *phy)
 static irqreturn_t mmp_pdma_chan_handler(int irq, void *dev_id)
 {
 	struct mmp_pdma_phy *phy = dev_id;
+	struct mmp_pdma_chan *vchan;
 
 	if (clear_chan_irq(phy) != 0)
 		return IRQ_NONE;
 
-	tasklet_schedule(&phy->vchan->tasklet);
+	vchan = READ_ONCE(phy->vchan);
+	if (!vchan)
+		return IRQ_HANDLED;
+
+	tasklet_schedule(&vchan->tasklet);
 	return IRQ_HANDLED;
 }
 
@@ -427,7 +434,7 @@ static struct mmp_pdma_phy *lookup_phy(struct mmp_pdma_chan *pchan)
 				continue;
 			phy = &pdev->phy[i];
 			if (!phy->vchan) {
-				phy->vchan = pchan;
+				WRITE_ONCE(phy->vchan, pchan);
 				found = phy;
 				goto out_unlock;
 			}
@@ -453,7 +460,7 @@ static void mmp_pdma_free_phy(struct mmp_pdma_chan *pchan)
 	writel(0, pchan->phy->base + reg);
 
 	spin_lock_irqsave(&pdev->phy_lock, flags);
-	pchan->phy->vchan = NULL;
+	WRITE_ONCE(pchan->phy->vchan, NULL);
 	pchan->phy = NULL;
 	spin_unlock_irqrestore(&pdev->phy_lock, flags);
 }
-- 
2.51.0