| Message ID | 20220512091327.349563-1-v.v.mitrofanov@yadro.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | dmaengine: sf-pdma: Add multithread support for a DMA channel | expand |
On 5/12/2022 2:13 AM, Viacheslav Mitrofanov wrote: > 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 it's value only when it has With the current fix a descriptor ... s/it's/its/ > 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 I suggest a '.' here instead of ',' DJ > 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> > --- > 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 f12606aeff87..70bb032c59c2 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 == NULL) && 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); > } >
diff --git a/drivers/dma/sf-pdma/sf-pdma.c b/drivers/dma/sf-pdma/sf-pdma.c index f12606aeff87..70bb032c59c2 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 == NULL) && 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); }
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 it's 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> --- drivers/dma/sf-pdma/sf-pdma.c | 44 ++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 14 deletions(-)