async_tx: remove walk of tx->parent chain in dma_wait_for_async_tx

We currently walk the parent chain when waiting for a given tx to
complete however this walk may race with the driver cleanup routine.
The routines in async_raid6_recov.c may fall back to the synchronous
path at any point so we need to be prepared to call async_tx_quiesce()
(which calls  dma_wait_for_async_tx).  To remove the ->parent walk we
guarantee that every time a dependency is attached ->issue_pending() is
invoked, then we can simply poll the initial descriptor until
completion.

This also allows for a lighter weight 'issue pending' implementation as
there is no longer a requirement to iterate through all the channels'
->issue_pending() routines as long as operations have been submitted in
an ordered chain.  async_tx_issue_pending() is added for this case.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 10 insertions, 35 deletions

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 6781e8f3c064..e002e0e0d055 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -934,49 +934,24 @@ EXPORT_SYMBOL(dma_async_tx_descriptor_init);
 
 /* dma_wait_for_async_tx - spin wait for a transaction to complete
  * @tx: in-flight transaction to wait on
- *
- * This routine assumes that tx was obtained from a call to async_memcpy,
- * async_xor, async_memset, etc which ensures that tx is "in-flight" (prepped
- * and submitted).  Walking the parent chain is only meant to cover for DMA
- * drivers that do not implement the DMA_INTERRUPT capability and may race with
- * the driver's descriptor cleanup routine.
  */
 enum dma_status
 dma_wait_for_async_tx(struct dma_async_tx_descriptor *tx)
 {
-        enum dma_status status;
-        struct dma_async_tx_descriptor *iter;
-        struct dma_async_tx_descriptor *parent;
+        unsigned long dma_sync_wait_timeout = jiffies + msecs_to_jiffies(5000);
 
         if (!tx)
                 return DMA_SUCCESS;
 
-        WARN_ONCE(tx->parent, "%s: speculatively walking dependency chain for"
-                  " %s\n", __func__, dma_chan_name(tx->chan));
-
-        /* poll through the dependency chain, return when tx is complete */
-        do {
-                iter = tx;
-
-                /* find the root of the unsubmitted dependency chain */
-                do {
-                        parent = iter->parent;
-                        if (!parent)
-                                break;
-                        else
-                                iter = parent;
-                } while (parent);
-
-                /* there is a small window for ->parent == NULL and
-                 * ->cookie == -EBUSY
-                 */
-                while (iter->cookie == -EBUSY)
-                        cpu_relax();
-
-                status = dma_sync_wait(iter->chan, iter->cookie);
-        } while (status == DMA_IN_PROGRESS || (iter != tx));
-
-        return status;
+        while (tx->cookie == -EBUSY) {
+                if (time_after_eq(jiffies, dma_sync_wait_timeout)) {
+                        pr_err("%s timeout waiting for descriptor submission\n",
+                                __func__);
+                        return DMA_ERROR;
+                }
+                cpu_relax();
+        }
+        return dma_sync_wait(tx->chan, tx->cookie);
 }
 EXPORT_SYMBOL_GPL(dma_wait_for_async_tx);