powerpc/512x: try to free dma descriptors in case of allocation failure

Currently completed descriptors are processed in the tasklet. This can
lead to dead lock in case of CONFIG_NET_DMA enabled (new requests are
submitted from softirq context and dma_memcpy_to_iovec() busy loops until
the requests is submitted). To prevent this we should process completed
descriptors from the allocation failure path in prepare_memcpy too.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Cc: Piotr Ziecik <kosmo@semihalf.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 45 insertions, 34 deletions

diff --git a/drivers/dma/mpc512x_dma.c b/drivers/dma/mpc512x_dma.c
index 97b92ecb1427..59c270192ccc 100644
--- a/drivers/dma/mpc512x_dma.c
+++ b/drivers/dma/mpc512x_dma.c
@@ -328,19 +328,55 @@ static irqreturn_t mpc_dma_irq(int irq, void *data)
         return IRQ_HANDLED;
 }
 
-/* DMA Tasklet */
-static void mpc_dma_tasklet(unsigned long data)
+/* proccess completed descriptors */
+static void mpc_dma_process_completed(struct mpc_dma *mdma)
 {
-        struct mpc_dma *mdma = (void *)data;
         dma_cookie_t last_cookie = 0;
         struct mpc_dma_chan *mchan;
         struct mpc_dma_desc *mdesc;
         struct dma_async_tx_descriptor *desc;
         unsigned long flags;
         LIST_HEAD(list);
-        uint es;
         int i;
 
+        for (i = 0; i < mdma->dma.chancnt; i++) {
+                mchan = &mdma->channels[i];
+
+                /* Get all completed descriptors */
+                spin_lock_irqsave(&mchan->lock, flags);
+                if (!list_empty(&mchan->completed))
+                        list_splice_tail_init(&mchan->completed, &list);
+                spin_unlock_irqrestore(&mchan->lock, flags);
+
+                if (list_empty(&list))
+                        continue;
+
+                /* Execute callbacks and run dependencies */
+                list_for_each_entry(mdesc, &list, node) {
+                        desc = &mdesc->desc;
+
+                        if (desc->callback)
+                                desc->callback(desc->callback_param);
+
+                        last_cookie = desc->cookie;
+                        dma_run_dependencies(desc);
+                }
+
+                /* Free descriptors */
+                spin_lock_irqsave(&mchan->lock, flags);
+                list_splice_tail_init(&list, &mchan->free);
+                mchan->completed_cookie = last_cookie;
+                spin_unlock_irqrestore(&mchan->lock, flags);
+        }
+}
+
+/* DMA Tasklet */
+static void mpc_dma_tasklet(unsigned long data)
+{
+        struct mpc_dma *mdma = (void *)data;
+        unsigned long flags;
+        uint es;
+
         spin_lock_irqsave(&mdma->error_status_lock, flags);
         es = mdma->error_status;
         mdma->error_status = 0;
@@ -379,35 +415,7 @@ static void mpc_dma_tasklet(unsigned long data)
                         dev_err(mdma->dma.dev, "- Destination Bus Error\n");
         }
 
-        for (i = 0; i < mdma->dma.chancnt; i++) {
-                mchan = &mdma->channels[i];
-
-                /* Get all completed descriptors */
-                spin_lock_irqsave(&mchan->lock, flags);
-                if (!list_empty(&mchan->completed))
-                        list_splice_tail_init(&mchan->completed, &list);
-                spin_unlock_irqrestore(&mchan->lock, flags);
-
-                if (list_empty(&list))
-                        continue;
-
-                /* Execute callbacks and run dependencies */
-                list_for_each_entry(mdesc, &list, node) {
-                        desc = &mdesc->desc;
-
-                        if (desc->callback)
-                                desc->callback(desc->callback_param);
-
-                        last_cookie = desc->cookie;
-                        dma_run_dependencies(desc);
-                }
-
-                /* Free descriptors */
-                spin_lock_irqsave(&mchan->lock, flags);
-                list_splice_tail_init(&list, &mchan->free);
-                mchan->completed_cookie = last_cookie;
-                spin_unlock_irqrestore(&mchan->lock, flags);
-        }
+        mpc_dma_process_completed(mdma);
 }
 
 /* Submit descriptor to hardware */
@@ -587,8 +595,11 @@ mpc_dma_prep_memcpy(struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
         }
         spin_unlock_irqrestore(&mchan->lock, iflags);
 
-        if (!mdesc)
+        if (!mdesc) {
+                /* try to free completed descriptors */
+                mpc_dma_process_completed(mdma);
                 return NULL;
+        }
 
         mdesc->error = 0;
         tcd = mdesc->tcd;