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    Subject[PATCH 5.10 307/545] dmaengine: sf-pdma: Add multithread support for a DMA channel
    Date
    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 1cd2d7df9715..5c615a8b514b 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


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