@@ -35,6 +35,7 @@ struct virt_dma_chan {
struct list_head desc_completed;
struct virt_dma_desc *cyclic;
+ struct virt_dma_desc *vd_terminated;
};
static inline struct virt_dma_chan *to_virt_chan(struct dma_chan *chan)
@@ -129,6 +130,25 @@ static inline void vchan_cyclic_callback(struct virt_dma_desc *vd)
tasklet_schedule(&vc->task);
}
+/**
+ * vchan_terminate_vdesc - Disable pending cyclic callback
+ * @vd: virtual descriptor to be terminated
+ *
+ * vc.lock must be held by caller
+ */
+static inline void vchan_terminate_vdesc(struct virt_dma_desc *vd)
+{
+ struct virt_dma_chan *vc = to_virt_chan(vd->tx.chan);
+
+ /* free up stuck descriptor */
+ if (vc->vd_terminated)
+ vchan_vdesc_fini(vc->vd_terminated);
+
+ vc->vd_terminated = vd;
+ if (vc->cyclic == vd)
+ vc->cyclic = NULL;
+}
+
/**
* vchan_next_desc - peek at the next descriptor to be processed
* @vc: virtual channel to obtain descriptor from
@@ -182,10 +202,20 @@ static inline void vchan_free_chan_resources(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.
*/
static inline void vchan_synchronize(struct virt_dma_chan *vc)
{
+ unsigned long flags;
+
tasklet_kill(&vc->task);
+
+ spin_lock_irqsave(&vc->lock, flags);
+ if (vc->vd_terminated) {
+ vchan_vdesc_fini(vc->vd_terminated);
+ vc->vd_terminated = NULL;
+ }
+ spin_unlock_irqrestore(&vc->lock, flags);
}
#endif
Even with the introduced vchan_synchronize() we can face race when terminating a cyclic transfer. If the terminate_all is called after the interrupt handler called vchan_cyclic_callback(), but before the vchan_complete tasklet is called: vc->cyclic is set to the cyclic descriptor, but the descriptor itself was freed up in the driver's terminate_all() callback. When the vhan_complete() is executed it will try to fetch the vc->cyclic vdesc, but the pointer is pointing now to uninitialized memory leading to (hard to reproduce) kernel crash. In order to fix this, drivers should: - call vchan_terminate_vdesc() from their terminate_all callback instead calling their free_desc function to free up the descriptor. - implement device_synchronize callback and call vchan_synchronize(). This way we can make sure that the descriptor is only going to be freed up after the vchan_callback was executed in a safe manner. Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com> --- drivers/dma/virt-dma.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)