[3.13.y-ckt stable] Patch "dmaengine: mv_xor: bug fix for racing condition in descriptors cleanup" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    dmaengine: mv_xor: bug fix for racing condition in descriptors cleanup

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt24.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From fc394213abd897076eee168c4f69ee3dc0e49f27 Mon Sep 17 00:00:00 2001
From: Lior Amsalem <alior at marvell.com>
Date: Tue, 26 May 2015 15:07:32 +0200
Subject: dmaengine: mv_xor: bug fix for racing condition in descriptors
 cleanup

commit 9136291f1dbc1d4d1cacd2840fb35f4f3ce16c46 upstream.

This patch fixes a bug in the XOR driver where the cleanup function can be
called and free descriptors that never been processed by the engine (which
result in data errors).

The cleanup function will free descriptors based on the ownership bit in
the descriptors.

Fixes: ff7b04796d98 ("dmaengine: DMA engine driver for Marvell XOR engine")
Signed-off-by: Lior Amsalem <alior at marvell.com>
Signed-off-by: Maxime Ripard <maxime.ripard at free-electrons.com>
Reviewed-by: Ofer Heifetz <oferh at marvell.com>
Signed-off-by: Vinod Koul <vinod.koul at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/dma/mv_xor.c | 72 +++++++++++++++++++++++++++++++++-------------------
 drivers/dma/mv_xor.h |  1 +
 2 files changed, 47 insertions(+), 26 deletions(-)

diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
index 29c8a06..b01f711 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -316,7 +316,8 @@ static void __mv_xor_slot_cleanup(struct mv_xor_chan *mv_chan)
 	dma_cookie_t cookie = 0;
 	int busy = mv_chan_is_busy(mv_chan);
 	u32 current_desc = mv_chan_get_current_desc(mv_chan);
-	int seen_current = 0;
+	int current_cleaned = 0;
+	struct mv_xor_desc *hw_desc;

 	dev_dbg(mv_chan_to_devp(mv_chan), "%s %d\n", __func__, __LINE__);
 	dev_dbg(mv_chan_to_devp(mv_chan), "current_desc %x\n", current_desc);
@@ -328,38 +329,57 @@ static void __mv_xor_slot_cleanup(struct mv_xor_chan *mv_chan)

 	list_for_each_entry_safe(iter, _iter, &mv_chan->chain,
 					chain_node) {
-		prefetch(_iter);
-		prefetch(&_iter->async_tx);

-		/* do not advance past the current descriptor loaded into the
-		 * hardware channel, subsequent descriptors are either in
-		 * process or have not been submitted
-		 */
-		if (seen_current)
-			break;
+		/* clean finished descriptors */
+		hw_desc = iter->hw_desc;
+		if (hw_desc->status & XOR_DESC_SUCCESS) {
+			cookie = mv_xor_run_tx_complete_actions(iter, mv_chan,
+								cookie);

-		/* stop the search if we reach the current descriptor and the
-		 * channel is busy
-		 */
-		if (iter->async_tx.phys == current_desc) {
-			seen_current = 1;
-			if (busy)
+			/* done processing desc, clean slot */
+			mv_xor_clean_slot(iter, mv_chan);
+
+			/* break if we did cleaned the current */
+			if (iter->async_tx.phys == current_desc) {
+				current_cleaned = 1;
+				break;
+			}
+		} else {
+			if (iter->async_tx.phys == current_desc) {
+				current_cleaned = 0;
 				break;
+			}
 		}
-
-		cookie = mv_xor_run_tx_complete_actions(iter, mv_chan, cookie);
-
-		if (mv_xor_clean_slot(iter, mv_chan))
-			break;
 	}

 	if ((busy == 0) && !list_empty(&mv_chan->chain)) {
-		struct mv_xor_desc_slot *chain_head;
-		chain_head = list_entry(mv_chan->chain.next,
-					struct mv_xor_desc_slot,
-					chain_node);
-
-		mv_xor_start_new_chain(mv_chan, chain_head);
+		if (current_cleaned) {
+			/*
+			 * current descriptor cleaned and removed, run
+			 * from list head
+			 */
+			iter = list_entry(mv_chan->chain.next,
+					  struct mv_xor_desc_slot,
+					  chain_node);
+			mv_xor_start_new_chain(mv_chan, iter);
+		} else {
+			if (!list_is_last(&iter->chain_node, &mv_chan->chain)) {
+				/*
+				 * descriptors are still waiting after
+				 * current, trigger them
+				 */
+				iter = list_entry(iter->chain_node.next,
+						  struct mv_xor_desc_slot,
+						  chain_node);
+				mv_xor_start_new_chain(mv_chan, iter);
+			} else {
+				/*
+				 * some descriptors are still waiting
+				 * to be cleaned
+				 */
+				tasklet_schedule(&mv_chan->irq_tasklet);
+			}
+		}
 	}

 	if (cookie > 0)
diff --git a/drivers/dma/mv_xor.h b/drivers/dma/mv_xor.h
index d074922..5d14e4b 100644
--- a/drivers/dma/mv_xor.h
+++ b/drivers/dma/mv_xor.h
@@ -33,6 +33,7 @@
 #define XOR_OPERATION_MODE_XOR		0
 #define XOR_OPERATION_MODE_MEMCPY	2
 #define XOR_DESCRIPTOR_SWAP		BIT(14)
+#define XOR_DESC_SUCCESS		0x40000000

 #define XOR_CURR_DESC(chan)	(chan->mmr_high_base + 0x10 + (chan->idx * 4))
 #define XOR_NEXT_DESC(chan)	(chan->mmr_high_base + 0x00 + (chan->idx * 4))
--
1.9.1