Commit b2cc5c46 authored by Viacheslav Mitrofanov's avatar Viacheslav Mitrofanov Committed by Vinod Koul
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dmaengine: sf-pdma: Add multithread support for a DMA channel 



When we get a DMA channel and try to use it in multiple threads it
will cause oops and hanging the system.

% echo 64 > /sys/module/dmatest/parameters/threads_per_chan
% echo 10000 > /sys/module/dmatest/parameters/iterations
% echo 1 > /sys/module/dmatest/parameters/run
[   89.480664] Unable to handle kernel NULL pointer dereference at virtual
               address 00000000000000a0
[   89.488725] Oops [#1]
[   89.494708] CPU: 2 PID: 1008 Comm: dma0chan0-copy0 Not tainted
               5.17.0-rc5
[   89.509385] epc : vchan_find_desc+0x32/0x46
[   89.513553]  ra : sf_pdma_tx_status+0xca/0xd6

This happens because of data race. Each thread rewrite channels's
descriptor as soon as device_prep_dma_memcpy() is called. It leads to the
situation when the driver thinks that it uses right descriptor that
actually is freed or substituted for other one.

With current fixes a descriptor changes its value only when it has
been used. A new descriptor is acquired from vc->desc_issued queue that
is already filled with descriptors that are ready to be sent. Threads
have no direct access to DMA channel descriptor. Now it is just possible
to queue a descriptor for further processing.

Fixes: 6973886a ("dmaengine: sf-pdma: add platform DMA support for HiFive Unleashed A00")
Signed-off-by: default avatarViacheslav Mitrofanov <v.v.mitrofanov@yadro.com>
Link: https://lore.kernel.org/r/20220701082942.12835-1-v.v.mitrofanov@yadro.com


Signed-off-by: default avatarVinod Koul <vkoul@kernel.org>
parent 4ce653d7

drivers/dma/sf-pdma/sf-pdma.c

+30 −14
Original line number Diff line number Diff line
@@ -52,16 +52,6 @@ static inline struct sf_pdma_desc *to_sf_pdma_desc(struct virt_dma_desc *vd) 
static struct sf_pdma_desc *sf_pdma_alloc_desc(struct sf_pdma_chan *chan)

{

	struct sf_pdma_desc *desc;

	unsigned long flags;



	spin_lock_irqsave(&chan->lock, flags);



	if (chan->desc && !chan->desc->in_use) {

		spin_unlock_irqrestore(&chan->lock, flags);

		return chan->desc;

	}



	spin_unlock_irqrestore(&chan->lock, flags);



	desc = kzalloc(sizeof(*desc), GFP_NOWAIT);

	if (!desc)
@@ -111,7 +101,6 @@ sf_pdma_prep_dma_memcpy(struct dma_chan *dchan, dma_addr_t dest, dma_addr_t src, 
	desc->async_tx = vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);



	spin_lock_irqsave(&chan->vchan.lock, iflags);

	chan->desc = desc;

	sf_pdma_fill_desc(desc, dest, src, len);

	spin_unlock_irqrestore(&chan->vchan.lock, iflags);
@@ -170,11 +159,17 @@ static size_t sf_pdma_desc_residue(struct sf_pdma_chan *chan, 
	unsigned long flags;

	u64 residue = 0;

	struct sf_pdma_desc *desc;

	struct dma_async_tx_descriptor *tx;

	struct dma_async_tx_descriptor *tx = NULL;



	spin_lock_irqsave(&chan->vchan.lock, flags);



	tx = &chan->desc->vdesc.tx;

	list_for_each_entry(vd, &chan->vchan.desc_submitted, node)

		if (vd->tx.cookie == cookie)

			tx = &vd->tx;



	if (!tx)

		goto out;



	if (cookie == tx->chan->completed_cookie)

		goto out;
@@ -241,6 +236,19 @@ static void sf_pdma_enable_request(struct sf_pdma_chan *chan) 
	writel(v, regs->ctrl);

}



static struct sf_pdma_desc *sf_pdma_get_first_pending_desc(struct sf_pdma_chan *chan)

{

	struct virt_dma_chan *vchan = &chan->vchan;

	struct virt_dma_desc *vdesc;



	if (list_empty(&vchan->desc_issued))

		return NULL;



	vdesc = list_first_entry(&vchan->desc_issued, struct virt_dma_desc, node);



	return container_of(vdesc, struct sf_pdma_desc, vdesc);

}



static void sf_pdma_xfer_desc(struct sf_pdma_chan *chan)

{

	struct sf_pdma_desc *desc = chan->desc;
@@ -268,8 +276,11 @@ static void sf_pdma_issue_pending(struct dma_chan *dchan) 


	spin_lock_irqsave(&chan->vchan.lock, flags);



	if (vchan_issue_pending(&chan->vchan) && chan->desc)

	if (!chan->desc && vchan_issue_pending(&chan->vchan)) {

		/* vchan_issue_pending has made a check that desc in not NULL */

		chan->desc = sf_pdma_get_first_pending_desc(chan);

		sf_pdma_xfer_desc(chan);

	}



	spin_unlock_irqrestore(&chan->vchan.lock, flags);

}
@@ -298,6 +309,11 @@ static void sf_pdma_donebh_tasklet(struct tasklet_struct *t) 
	spin_lock_irqsave(&chan->vchan.lock, flags);

	list_del(&chan->desc->vdesc.node);

	vchan_cookie_complete(&chan->desc->vdesc);



	chan->desc = sf_pdma_get_first_pending_desc(chan);

	if (chan->desc)

		sf_pdma_xfer_desc(chan);



	spin_unlock_irqrestore(&chan->vchan.lock, flags);

}