From: Viacheslav Mitrofanov v.v.mitrofanov@yadro.com
[ Upstream commit b2cc5c465c2cb8ab697c3fd6583c614e3f6cfbcc ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/dma/sf-pdma/sf-pdma.c | 44 ++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 14 deletions(-)
diff --git a/drivers/dma/sf-pdma/sf-pdma.c b/drivers/dma/sf-pdma/sf-pdma.c index db5a4ef76077..4f8b8498c5c6 100644 --- 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); }