[PATCH 5.18 0730/1095] dmaengine: sf-pdma: Add multithread support for a DMA channel

Greg Kroah-Hartman
2022-08-15T22:09:07Z

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 f12606aeff87..ab0ad7a2f201 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);
}

--
2.35.1