[PATCH 06/10] dmaengine: at_hdmac: Fix deadlocks

From: <Tudor.Ambarus@microchip.com>
To: <Ludovic.Desroches@microchip.com>, <dan.j.williams@intel.com>,
	<vkoul@kernel.org>
Cc: <dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<Tudor.Ambarus@microchip.com>
Subject: [PATCH 06/10] dmaengine: at_hdmac: Fix deadlocks
Date: Thu, 23 Jan 2020 14:03:11 +0000	[thread overview]
Message-ID: <20200123140237.125799-6-tudor.ambarus@microchip.com> (raw)
In-Reply-To: <20200123140237.125799-1-tudor.ambarus@microchip.com>

From: Tudor Ambarus <tudor.ambarus@microchip.com>

Fix the following deadlocks:
1/ atc_handle_cyclic() and atc_chain_complete() called
dmaengine_desc_get_callback_invoke() while wrongly holding the
atchan->lock. Clients can set the callback to dmaengine_terminate_sync()
which will end up trying to get the same lock, thus a deadlock occurred.
2/ dma_run_dependencies() was called with the atchan->lock held, but the
method calls device_issue_pending() which tries to get the same lock,
and so a deadlock occurred.

The driver must not hold the lock when invoking the callback or when
running dependencies. Releasing the spinlock within a called function
before calling the callback is not a nice thing to do -> called functions
become non-atomic when called within an atomic region. Thus the lock is
now taken in the child routines whereever is needed.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
---
 drivers/dma/at_hdmac.c | 74 ++++++++++++++++++++++--------------------
 1 file changed, 39 insertions(+), 35 deletions(-)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 8e8e04bd1b28..73a20780744b 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -426,17 +426,19 @@ static int atc_get_bytes_left(struct dma_chan *chan, dma_cookie_t cookie)
  * atc_chain_complete - finish work for one transaction chain
  * @atchan: channel we work on
  * @desc: descriptor at the head of the chain we want do complete
- *
- * Called with atchan->lock held and bh disabled */
+ */
 static void
 atc_chain_complete(struct at_dma_chan *atchan, struct at_desc *desc)
 {
 	struct dma_async_tx_descriptor	*txd = &desc->txd;
 	struct at_dma			*atdma = to_at_dma(atchan->chan_common.device);
+	unsigned long flags;
 
 	dev_vdbg(chan2dev(&atchan->chan_common),
 		"descriptor %u complete\n", txd->cookie);
 
+	spin_lock_irqsave(&atchan->lock, flags);
+
 	/* mark the descriptor as complete for non cyclic cases only */
 	if (!atc_chan_is_cyclic(atchan))
 		dma_cookie_complete(txd);
@@ -453,16 +455,13 @@ atc_chain_complete(struct at_dma_chan *atchan, struct at_desc *desc)
 	/* move myself to free_list */
 	list_move(&desc->desc_node, &atchan->free_list);
 
+	spin_unlock_irqrestore(&atchan->lock, flags);
+
 	dma_descriptor_unmap(txd);
 	/* for cyclic transfers,
 	 * no need to replay callback function while stopping */
-	if (!atc_chan_is_cyclic(atchan)) {
-		/*
-		 * The API requires that no submissions are done from a
-		 * callback, so we don't need to drop the lock here
-		 */
+	if (!atc_chan_is_cyclic(atchan))
 		dmaengine_desc_get_callback_invoke(txd, NULL);
-	}
 
 	dma_run_dependencies(txd);
 }
@@ -480,9 +479,12 @@ static void atc_complete_all(struct at_dma_chan *atchan)
 {
 	struct at_desc *desc, *_desc;
 	LIST_HEAD(list);
+	unsigned long flags;
 
 	dev_vdbg(chan2dev(&atchan->chan_common), "complete all\n");
 
+	spin_lock_irqsave(&atchan->lock, flags);
+
 	/*
 	 * Submit queued descriptors ASAP, i.e. before we go through
 	 * the completed ones.
@@ -494,6 +496,8 @@ static void atc_complete_all(struct at_dma_chan *atchan)
 	/* empty queue list by moving descriptors (if any) to active_list */
 	list_splice_init(&atchan->queue, &atchan->active_list);
 
+	spin_unlock_irqrestore(&atchan->lock, flags);
+
 	list_for_each_entry_safe(desc, _desc, &list, desc_node)
 		atc_chain_complete(atchan, desc);
 }
@@ -501,38 +505,44 @@ static void atc_complete_all(struct at_dma_chan *atchan)
 /**
  * atc_advance_work - at the end of a transaction, move forward
  * @atchan: channel where the transaction ended
- *
- * Called with atchan->lock held and bh disabled
  */
 static void atc_advance_work(struct at_dma_chan *atchan)
 {
+	unsigned long flags;
+	int ret;
+
 	dev_vdbg(chan2dev(&atchan->chan_common), "advance_work\n");
 
-	if (atc_chan_is_enabled(atchan))
+	spin_lock_irqsave(&atchan->lock, flags);
+	ret = atc_chan_is_enabled(atchan);
+	spin_unlock_irqrestore(&atchan->lock, flags);
+	if (ret)
 		return;
 
 	if (list_empty(&atchan->active_list) ||
-	    list_is_singular(&atchan->active_list)) {
-		atc_complete_all(atchan);
-	} else {
-		atc_chain_complete(atchan, atc_first_active(atchan));
-		/* advance work */
-		atc_dostart(atchan, atc_first_active(atchan));
-	}
+	    list_is_singular(&atchan->active_list))
+		return atc_complete_all(atchan);
+
+	atc_chain_complete(atchan, atc_first_active(atchan));
+
+	/* advance work */
+	spin_lock_irqsave(&atchan->lock, flags);
+	atc_dostart(atchan, atc_first_active(atchan));
+	spin_unlock_irqrestore(&atchan->lock, flags);
 }
 
 
 /**
  * atc_handle_error - handle errors reported by DMA controller
  * @atchan: channel where error occurs
- *
- * Called with atchan->lock held and bh disabled
  */
 static void atc_handle_error(struct at_dma_chan *atchan)
 {
 	struct at_desc *bad_desc;
 	struct at_desc *child;
+	unsigned long flags;
 
+	spin_lock_irqsave(&atchan->lock, flags);
 	/*
 	 * The descriptor currently at the head of the active list is
 	 * broked. Since we don't have any way to report errors, we'll
@@ -564,6 +574,8 @@ static void atc_handle_error(struct at_dma_chan *atchan)
 	list_for_each_entry(child, &bad_desc->tx_list, desc_node)
 		atc_dump_lli(atchan, &child->lli);
 
+	spin_unlock_irqrestore(&atchan->lock, flags);
+
 	/* Pretend the descriptor completed successfully */
 	atc_chain_complete(atchan, bad_desc);
 }
@@ -571,8 +583,6 @@ static void atc_handle_error(struct at_dma_chan *atchan)
 /**
  * atc_handle_cyclic - at the end of a period, run callback function
  * @atchan: channel used for cyclic operations
- *
- * Called with atchan->lock held and bh disabled
  */
 static void atc_handle_cyclic(struct at_dma_chan *atchan)
 {
@@ -591,17 +601,14 @@ static void atc_handle_cyclic(struct at_dma_chan *atchan)
 static void atc_tasklet(unsigned long data)
 {
 	struct at_dma_chan *atchan = (struct at_dma_chan *)data;
-	unsigned long flags;
 
-	spin_lock_irqsave(&atchan->lock, flags);
 	if (test_and_clear_bit(ATC_IS_ERROR, &atchan->status))
-		atc_handle_error(atchan);
-	else if (atc_chan_is_cyclic(atchan))
-		atc_handle_cyclic(atchan);
-	else
-		atc_advance_work(atchan);
+		return atc_handle_error(atchan);
 
-	spin_unlock_irqrestore(&atchan->lock, flags);
+	if (atc_chan_is_cyclic(atchan))
+		return atc_handle_cyclic(atchan);
+
+	atc_advance_work(atchan);
 }
 
 static irqreturn_t at_dma_interrupt(int irq, void *dev_id)
@@ -1437,6 +1444,8 @@ static int atc_terminate_all(struct dma_chan *chan)
 	list_splice_init(&atchan->queue, &list);
 	list_splice_init(&atchan->active_list, &list);
 
+	spin_unlock_irqrestore(&atchan->lock, flags);
+
 	/* Flush all pending and queued descriptors */
 	list_for_each_entry_safe(desc, _desc, &list, desc_node)
 		atc_chain_complete(atchan, desc);
@@ -1445,8 +1454,6 @@ static int atc_terminate_all(struct dma_chan *chan)
 	/* if channel dedicated to cyclic operations, free it */
 	clear_bit(ATC_IS_CYCLIC, &atchan->status);
 
-	spin_unlock_irqrestore(&atchan->lock, flags);
-
 	return 0;
 }
 
@@ -1507,7 +1514,6 @@ atc_tx_status(struct dma_chan *chan,
 static void atc_issue_pending(struct dma_chan *chan)
 {
 	struct at_dma_chan	*atchan = to_at_dma_chan(chan);
-	unsigned long		flags;
 
 	dev_vdbg(chan2dev(chan), "issue_pending\n");
 
@@ -1515,9 +1521,7 @@ static void atc_issue_pending(struct dma_chan *chan)
 	if (atc_chan_is_cyclic(atchan))
 		return;
 
-	spin_lock_irqsave(&atchan->lock, flags);
 	atc_advance_work(atchan);
-	spin_unlock_irqrestore(&atchan->lock, flags);
 }
 
 /**
-- 
2.23.0
