[PATCH 3.18 066/108] dmaengine: imx-dma: fix wrong callback invoke

[Greg Kroah-Hartman]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Leonid Iziumtsev <leonid.iziumtsev@xxxxxxxxx>

commit 341198eda723c8c1cddbb006a89ad9e362502ea2 upstream.

Once the "ld_queue" list is not empty, next descriptor will migrate
into "ld_active" list. The "desc" variable will be overwritten
during that transition. And later the dmaengine_desc_get_callback_invoke()
will use it as an argument. As result we invoke wrong callback.

That behaviour was in place since:
commit fcaaba6c7136 ("dmaengine: imx-dma: fix callback path in tasklet").
But after commit 4cd13c21b207 ("softirq: Let ksoftirqd do its job")
things got worse, since possible delay between tasklet_schedule()
from DMA irq handler and actual tasklet function execution got bigger.
And that gave more time for new DMA request to be submitted and
to be put into "ld_queue" list.

It has been noticed that DMA issue is causing problems for "mxc-mmc"
driver. While stressing the system with heavy network traffic and
writing/reading to/from sd card simultaneously the timeout may happen:

10013000.sdhci: mxcmci_watchdog: read time out (status = 0x30004900)

That often lead to file system corruption.

Signed-off-by: Leonid Iziumtsev <leonid.iziumtsev@xxxxxxxxx>
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/dma/imx-dma.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/dma/imx-dma.c
+++ b/drivers/dma/imx-dma.c
@@ -624,7 +624,7 @@ static void imxdma_tasklet(unsigned long
 {
 	struct imxdma_channel *imxdmac = (void *)data;
 	struct imxdma_engine *imxdma = imxdmac->imxdma;
-	struct imxdma_desc *desc;
+	struct imxdma_desc *desc, *next_desc;
 	unsigned long flags;
 
 	spin_lock_irqsave(&imxdma->lock, flags);
@@ -654,10 +654,10 @@ static void imxdma_tasklet(unsigned long
 	list_move_tail(imxdmac->ld_active.next, &imxdmac->ld_free);
 
 	if (!list_empty(&imxdmac->ld_queue)) {
-		desc = list_first_entry(&imxdmac->ld_queue, struct imxdma_desc,
-					node);
+		next_desc = list_first_entry(&imxdmac->ld_queue,
+					     struct imxdma_desc, node);
 		list_move_tail(imxdmac->ld_queue.next, &imxdmac->ld_active);
-		if (imxdma_xfer_desc(desc) < 0)
+		if (imxdma_xfer_desc(next_desc) < 0)
 			dev_warn(imxdma->dev, "%s: channel: %d couldn't xfer desc\n",
 				 __func__, imxdmac->channel);
 	}