[RFC patch] DMA engine/Langwell: clean up race of descriptor operations

[Hillf Danton]

There are three contexts that descriptors are migrated between lists under no
lock protection, which races with same operations in other contexts.

Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
---
 drivers/dma/intel_mid_dma.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/intel_mid_dma.c b/drivers/dma/intel_mid_dma.c
index f653517..e39be42 100644
--- a/drivers/dma/intel_mid_dma.c
+++ b/drivers/dma/intel_mid_dma.c
@@ -301,10 +301,11 @@ static void midc_descriptor_complete(struct
intel_mid_dma_chan *midc,
 		else
 			desc->current_lli = 0;
 	}
-	spin_unlock_bh(&midc->lock);
 	if (callback_txd) {
+		spin_unlock_bh(&midc->lock);
 		pr_debug("MDMA: TXD callback set ... calling\n");
 		callback_txd(param_txd);
+		spin_lock_bh(&midc->lock);
 	}
 	if (midc->raw_tfr) {
 		desc->status = DMA_SUCCESS;
@@ -316,8 +317,6 @@ static void midc_descriptor_complete(struct
intel_mid_dma_chan *midc,
 		list_move(&desc->desc_node, &midc->free_list);
 		midc->busy = false;
 	}
-	spin_lock_bh(&midc->lock);
-
 }
 /**
  * midc_scan_descriptors -		check the descriptors in channel
@@ -491,7 +490,9 @@ static enum dma_status
intel_mid_dma_tx_status(struct dma_chan *chan,

 	ret = dma_async_is_complete(cookie, last_complete, last_used);
 	if (ret != DMA_SUCCESS) {
+		spin_lock_bh(&midc->lock);
 		midc_scan_descriptors(to_middma_device(chan->device), midc);
+		spin_unlock_bh(&midc->lock);

 		last_complete = midc->completed;
 		last_used = chan->cookie;
@@ -561,7 +562,6 @@ static int intel_mid_dma_device_control(struct
dma_chan *chan,
 	disable_dma_interrupt(midc);
 	midc->descs_allocated = 0;

-	spin_unlock_bh(&midc->lock);
 	list_for_each_entry_safe(desc, _desc, &midc->active_list, desc_node) {
 		if (desc->lli != NULL) {
 			pci_pool_free(desc->lli_pool, desc->lli,
@@ -570,6 +570,7 @@ static int intel_mid_dma_device_control(struct
dma_chan *chan,
 		}
 		list_move(&desc->desc_node, &midc->free_list);
 	}
+	spin_unlock_bh(&midc->lock);
 	return 0;
 }
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