[PATCH 3/4] dmaengine: dmatest: Terminate channel before freeing threads

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

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

On a channel shared by multiple threads, the completion callbacks run from
one tasklet, and dmaengine_terminate_sync() flushes it. Freeing a thread
before that flush can leave a pending callback pointing at freed memory
(dmatest_callback() reads thread->done).

Stop all channel threads and then flush the channel before freeing the
threads.

Fixes: 6f6a23a213be ("dmaengine: dmatest: move callback wait queue to thread context")
Assisted-by: Claude:claude-opus-4-8 [Claude-Code]
Signed-off-by: Nathan Lynch <nathan.lynch@amd.com>
---
 drivers/dma/dmatest.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
index 3267c7e86f5d..0d7752c2451a 100644
--- a/drivers/dma/dmatest.c
+++ b/drivers/dma/dmatest.c
@@ -959,18 +959,23 @@ static void dmatest_cleanup_channel(struct dmatest_chan *dtc)
 	struct dmatest_thread	*_thread;
 	int			ret;
 
-	list_for_each_entry_safe(thread, _thread, &dtc->threads, node) {
+	/* stop all threads first */
+	list_for_each_entry(thread, &dtc->threads, node) {
 		ret = kthread_stop(thread->task);
 		pr_debug("thread %s exited with status %d\n",
 			 thread->task->comm, ret);
+	}
+
+	/* flush the channel (e.g. vchan_synchronize() -> tasklet_kill()) */
+	dmaengine_terminate_sync(dtc->chan);
+
+	/* now it is safe to free the thread memory */
+	list_for_each_entry_safe(thread, _thread, &dtc->threads, node) {
 		list_del(&thread->node);
 		put_task_struct(thread->task);
 		kfree(thread);
 	}
 
-	/* terminate all transfers on specified channels */
-	dmaengine_terminate_sync(dtc->chan);
-
 	kfree(dtc);
 }
 

-- 
2.54.0