[PATCH v3 4/4] dmaengine: dw: synchronize completion callbacks

[James Hilliard <james.hilliard1@gmail.com>]

The controller tasklet can detach completed descriptors and invoke their
callbacks outside the channel lock. Terminating the channel does not wait
for those callbacks, and there is no device_synchronize hook. A client can
therefore reuse callback state or release its buffers after
dmaengine_synchronize() while an old callback still uses them.

Disable and re-enable the controller tasklet from device_synchronize,
outside the channel lock. Disabling waits for an executing tasklet,
including descriptors it already removed from the channel lists. After
termination, a later tasklet run cannot acquire another descriptor from
the terminated channel. Clients must continue to exclude new submissions
on that channel until synchronization finishes.

The tasklet is shared, so other channels may schedule it while this wait
is in progress. Preserve those pending runs: tasklet_kill() temporarily
owns the scheduling bit and can consume a concurrent scheduling request,
leaving controller interrupts masked. The disable/enable pair leaves the
scheduling bit and pending tasklet queue intact. Other channels' hardware
transfers continue, though their callbacks may be briefly deferred.

Fixes: b36f09c3c441 ("dmaengine: Add transfer termination synchronization support")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/r/sashiko-outbox-180707@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/dma/dw/core.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 6d27af3c0f2d..d80be93f0c49 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -910,6 +910,19 @@ static int dwc_terminate_all(struct dma_chan *chan)
 	return 0;
 }
 
+static void dwc_synchronize(struct dma_chan *chan)
+{
+	struct dw_dma *dw = to_dw_dma(chan->device);
+
+	/*
+	 * Termination removes the channel's descriptors from the lists, but a
+	 * running tasklet may still own a completed descriptor and its callback.
+	 * Wait for that run without losing schedules from the other channels.
+	 */
+	tasklet_disable(&dw->tasklet);
+	tasklet_enable(&dw->tasklet);
+}
+
 static struct dw_desc *dwc_find_desc(struct dw_dma_chan *dwc, dma_cookie_t c)
 {
 	struct dw_desc *desc;
@@ -1318,6 +1331,7 @@ int do_dma_probe(struct dw_dma_chip *chip)
 	dw->dma.device_pause = dwc_pause;
 	dw->dma.device_resume = dwc_resume;
 	dw->dma.device_terminate_all = dwc_terminate_all;
+	dw->dma.device_synchronize = dwc_synchronize;
 
 	dw->dma.device_tx_status = dwc_tx_status;
 	dw->dma.device_issue_pending = dwc_issue_pending;

-- 
2.53.0