[PATCH 2/4] dmaengine: dmatest: Suppress bogus failures when stopping a run

[Nathan Lynch via B4 Relay <devnull+nathan.lynch.amd.com@kernel.org>]

From: Nathan Lynch <nathan.lynch@amd.com>

Writing 0 to the module 'run' attribute stops the test threads with
kthread_stop(), waking threads out of wait_event_freezable_timeout()
before the last transfer's completion callback has run. The stopping
thread samples the transfer status and then checks done->done at two
different instants, so the last transaction gets misreported two ways:

- "test timed out": the wait returns early with done->done still clear
  even though the transfer is simply still finishing — not a real
  timeout.

- "completion busy status": status is read as DMA_IN_PROGRESS a moment
  before the transfer completes and latches done->done, so the stale
  status is reported as a failure against a transfer that actually
  succeeded.

This is not a recent regression: the threads have used an interruptible,
freezable timeout wait since long before the wait queue was moved into
thread context by commit 6f6a23a213be ("dmaengine: dmatest: move callback
wait queue to thread context"), so a stop has always been able to wake
the wait before the final callback runs.

When kthread_should_stop() returns true, use dma_sync_wait() to settle
the pending transaction. Real errors still yield DMA_ERROR.

Assisted-by: Claude:claude-opus-4-8 [Claude-Code]
Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
---
 drivers/dma/dmatest.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
index 60bc448f42ee..3267c7e86f5d 100644
--- a/drivers/dma/dmatest.c
+++ b/drivers/dma/dmatest.c
@@ -702,6 +702,7 @@ static int dmatest_func(void *data)
 		struct dmaengine_unmap_data *um;
 		dma_addr_t *dsts;
 		unsigned int len;
+		bool stopping;
 
 		total_tests++;
 
@@ -839,6 +840,7 @@ static int dmatest_func(void *data)
 			status = dma_sync_wait(chan, cookie);
 			if (status == DMA_COMPLETE)
 				done->done = true;
+			stopping = kthread_should_stop();
 		} else {
 			dma_async_issue_pending(chan);
 
@@ -846,14 +848,19 @@ static int dmatest_func(void *data)
 					done->done,
 					msecs_to_jiffies(params->timeout));
 
-			status = dma_async_is_tx_complete(chan, cookie, NULL,
-							  NULL);
+			stopping = kthread_should_stop();
+			status = stopping ?
+				dma_sync_wait(chan, cookie) :
+				dma_async_is_tx_complete(chan, cookie, NULL, NULL);
 		}
 
 		if (!done->done) {
-			result("test timed out", total_tests, src->off, dst->off,
-			       len, 0);
-			goto error_unmap_continue;
+			/* stopping: dma_sync_wait() let the transfer finish, not a timeout */
+			if (!stopping) {
+				result("test timed out", total_tests, src->off,
+				       dst->off, len, 0);
+				goto error_unmap_continue;
+			}
 		} else if (status != DMA_COMPLETE &&
 			   !(dma_has_cap(DMA_COMPLETION_NO_ORDER,
 					 dev->cap_mask) &&

-- 
2.54.0