linux-kernel - [PATCH 3.19.y-ckt 106/251] dmaengine: mv_xor: bug fix for racing condition in descriptors cleanup

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Message-Id: <1437008972-9140-107-git-send-email-kamal@canonical.com>
Date:	Wed, 15 Jul 2015 18:07:07 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Lior Amsalem <alior@...vell.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 106/251] dmaengine: mv_xor: bug fix for racing condition in descriptors cleanup

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lior Amsalem <alior@...vell.com>

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@...vell.com>
Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
Reviewed-by: Ofer Heifetz <oferh@...vell.com>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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 d7ac558..794cfcb 100644
--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -277,7 +277,8 @@ 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);
@@ -289,38 +290,57 @@ 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 78edc7e..4fa0fe2 100644
--- a/drivers/dma/mv_xor.h
+++ b/drivers/dma/mv_xor.h
@@ -35,6 +35,7 @@
 #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_DESC_DMA_OWNED		BIT(31)
 #define XOR_DESC_EOD_INT_EN		BIT(31)
-- 
1.9.1

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