[PATCH v2 1/3] dmaengine: virt-dma: share deferred descriptor retirement

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

A cyclic callback can retain its descriptor after the tasklet drops the
virtual-channel lock. Collecting and freeing descriptors during atomic
termination does not wait for that callback, and clearing vc->cyclic alone
only cancels a callback which has not started.

Provide vchan_terminate_all() to clear the pending cyclic callback and
move all channel-owned descriptors to desc_terminated. This also retains
a cyclic descriptor moved to the completed list by an error path, without
requiring provider-specific descriptor-type checks. Already detached
completed descriptors remain owned by the tasklet.

vchan_synchronize() drains callbacks before freeing or recycling the
retired descriptors. Repeated termination leaves them on the terminated
list until that synchronization occurs.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
 drivers/dma/virt-dma.h | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
index abf2ae737c30..d3057fc85a9b 100644
--- a/drivers/dma/virt-dma.h
+++ b/drivers/dma/virt-dma.h
@@ -199,6 +199,24 @@ static inline void vchan_get_all_descriptors(struct virt_dma_chan *vc,
 	list_splice_tail_init(&vc->desc_terminated, head);
 }
 
+/**
+ * vchan_terminate_all - retire descriptors until callbacks have drained
+ * @vc: virtual channel to terminate
+ *
+ * The caller must hold vc.lock and prevent further callback publication.
+ * Descriptors detached by the completion tasklet remain owned by that tasklet.
+ * All other descriptors are retained until vchan_synchronize(), including any
+ * descriptor still referenced by an executing cyclic callback.
+ */
+static inline void vchan_terminate_all(struct virt_dma_chan *vc)
+{
+	LIST_HEAD(head);
+
+	vchan_get_all_descriptors(vc, &head);
+	vc->cyclic = NULL;
+	list_splice_tail_init(&head, &vc->desc_terminated);
+}
+
 static inline void vchan_free_chan_resources(struct virt_dma_chan *vc)
 {
 	struct virt_dma_desc *vd;
@@ -232,7 +250,7 @@ static inline const char *vchan_chan_name(struct virt_dma_chan *vc)
  * Makes sure that all scheduled or active callbacks have finished running. For
  * proper operation the caller has to ensure that no new callbacks are scheduled
  * after the invocation of this function started.
- * Free up the terminated cyclic descriptor to prevent memory leakage.
+ * Free or recycle terminated descriptors after their callbacks have drained.
  */
 static inline void vchan_synchronize(struct virt_dma_chan *vc)
 {

-- 
2.53.0