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: 6973886ad58e ("dmaengine: sf-pdma: add platform DMA support for HiFive Unleashed A00")
Signed-off-by: Viacheslav Mitrofanov <v.v.mitrofanov@yadro.com>
Link: https://lore.kernel.org/r/20220701082942.12835-1-v.v.mitrofanov@yadro.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/sf-pdma/sf-pdma.c b/drivers/dma/sf-pdma/sf-pdma.c
index db5a4ef7607734cf0576948c0029393ef516bd5b..4f8b8498c5c62acef1abad81f95c453cb9a4e2fd 100644 (file)
--- a/drivers/dma/sf-pdma/sf-pdma.c
+++ b/drivers/dma/sf-pdma/sf-pdma.c
@@ -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);
 }