dmaengine: provide a common 'issue_pending_all' implementation

async_tx and net_dma each have open-coded versions of issue_pending_all,
so provide a common routine in dmaengine.

The implementation needs to walk the global device list, so implement
rcu to allow dma_issue_pending_all to run lockless.  Clients protect
themselves from channel removal events by holding a dmaengine reference.

Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

5 files changed, 27 insertions, 24 deletions

diff --git a/crypto/async_tx/async_tx.c b/crypto/async_tx/async_tx.c
index b88bb1f608fc..2cdf7a0867b7 100644
--- a/crypto/async_tx/async_tx.c
+++ b/crypto/async_tx/async_tx.c
@@ -45,18 +45,6 @@ static DEFINE_SPINLOCK(async_tx_lock);
 
 static LIST_HEAD(async_tx_master_list);
 
-/* async_tx_issue_pending_all - start all transactions on all channels */
-void async_tx_issue_pending_all(void)
-{
-        struct dma_chan_ref *ref;
-
-        rcu_read_lock();
-        list_for_each_entry_rcu(ref, &async_tx_master_list, node)
-                ref->chan->device->device_issue_pending(ref->chan);
-        rcu_read_unlock();
-}
-EXPORT_SYMBOL_GPL(async_tx_issue_pending_all);
-
 static void
 free_dma_chan_ref(struct rcu_head *rcu)
 {
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 87a8cd4791ed..418eca28d472 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -70,6 +70,7 @@
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>
 #include <linux/jiffies.h>
+#include <linux/rculist.h>
 
 static DEFINE_MUTEX(dma_list_mutex);
 static LIST_HEAD(dma_device_list);
@@ -366,6 +367,26 @@ struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type)
 EXPORT_SYMBOL(dma_find_channel);
 
 /**
+ * dma_issue_pending_all - flush all pending operations across all channels
+ */
+void dma_issue_pending_all(void)
+{
+        struct dma_device *device;
+        struct dma_chan *chan;
+
+        WARN_ONCE(dmaengine_ref_count == 0,
+                  "client called %s without a reference", __func__);
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(device, &dma_device_list, global_node)
+                list_for_each_entry(chan, &device->channels, device_node)
+                        if (chan->client_count)
+                                device->device_issue_pending(chan);
+        rcu_read_unlock();
+}
+EXPORT_SYMBOL(dma_issue_pending_all);
+
+/**
  * nth_chan - returns the nth channel of the given capability
  * @cap: capability to match
  * @n: nth channel desired
@@ -490,7 +511,7 @@ void dma_async_client_register(struct dma_client *client)
                         err = dma_chan_get(chan);
                         if (err == -ENODEV) {
                                 /* module removed before we could use it */
-                                list_del_init(&device->global_node);
+                                list_del_rcu(&device->global_node);
                                 break;
                         } else if (err)
                                 pr_err("dmaengine: failed to get %s: (%d)\n",
@@ -635,7 +656,7 @@ int dma_async_device_register(struct dma_device *device)
                                 goto err_out;
                         }
                 }
-        list_add_tail(&device->global_node, &dma_device_list);
+        list_add_tail_rcu(&device->global_node, &dma_device_list);
         dma_channel_rebalance();
         mutex_unlock(&dma_list_mutex);
 
@@ -677,7 +698,7 @@ void dma_async_device_unregister(struct dma_device *device)
         struct dma_chan *chan;
 
         mutex_lock(&dma_list_mutex);
-        list_del(&device->global_node);
+        list_del_rcu(&device->global_node);
         dma_channel_rebalance();
         mutex_unlock(&dma_list_mutex);
 
diff --git a/include/linux/async_tx.h b/include/linux/async_tx.h
index 1c816775f135..45f6297821bd 100644
--- a/include/linux/async_tx.h
+++ b/include/linux/async_tx.h
@@ -59,7 +59,7 @@ enum async_tx_flags {
 };
 
 #ifdef CONFIG_DMA_ENGINE
-void async_tx_issue_pending_all(void);
+#define async_tx_issue_pending_all dma_issue_pending_all
 #ifdef CONFIG_ARCH_HAS_ASYNC_TX_FIND_CHANNEL
 #include <asm/async_tx.h>
 #else
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index b466f02e2433..57a43adfc39e 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -471,6 +471,7 @@ int dma_async_device_register(struct dma_device *device);
 void dma_async_device_unregister(struct dma_device *device);
 void dma_run_dependencies(struct dma_async_tx_descriptor *tx);
 struct dma_chan *dma_find_channel(enum dma_transaction_type tx_type);
+void dma_issue_pending_all(void);
 
 /* --- Helper iov-locking functions --- */
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 09c66a449da6..e40b0d57f8ff 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2635,14 +2635,7 @@ out:
          * There may not be any more sk_buffs coming right now, so push
          * any pending DMA copies to hardware
          */
-        if (!cpus_empty(net_dma.channel_mask)) {
-                int chan_idx;
-                for_each_cpu_mask_nr(chan_idx, net_dma.channel_mask) {
-                        struct dma_chan *chan = net_dma.channels[chan_idx];
-                        if (chan)
-                                dma_async_memcpy_issue_pending(chan);
-                }
-        }
+        dma_issue_pending_all();
 #endif
 
         return;