* [PATCH] dmaengine: sf-pdma: Add multithread support for a DMA channel
@ 2022-05-12 9:13 Viacheslav Mitrofanov
2022-05-12 17:01 ` Dave Jiang
0 siblings, 1 reply; 2+ messages in thread
From: Viacheslav Mitrofanov @ 2022-05-12 9:13 UTC (permalink / raw)
To: Green Wan, Vinod Koul, dmaengine, linux-kernel
Cc: david.abdurachmanov, linux, Viacheslav Mitrofanov
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(-)
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);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] dmaengine: sf-pdma: Add multithread support for a DMA channel
2022-05-12 9:13 [PATCH] dmaengine: sf-pdma: Add multithread support for a DMA channel Viacheslav Mitrofanov
@ 2022-05-12 17:01 ` Dave Jiang
0 siblings, 0 replies; 2+ messages in thread
From: Dave Jiang @ 2022-05-12 17:01 UTC (permalink / raw)
To: Viacheslav Mitrofanov, Green Wan, Vinod Koul, dmaengine, linux-kernel
Cc: david.abdurachmanov, linux
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);
> }
>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-05-12 17:01 ` Dave Jiang
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