Avoid hw_desc array overrun in dw-axi-dmac

BugLink: https://bugs.launchpad.net/bugs/2075154
[ Upstream commit 333e11bf47fa8d477db90e2900b1ed3c9ae9b697 ]

I have a use case where nr_buffers = 3 and in which each descriptor is composed by 3
segments, resulting in the DMA channel descs_allocated to be 9. Since axi_desc_put()
handles the hw_desc considering the descs_allocated, this scenario would result in a
kernel panic (hw_desc array will be overrun).

To fix this, the proposal is to add a new member to the axi_dma_desc structure,
where we keep the number of allocated hw_descs (axi_desc_alloc()) and use it in
axi_desc_put() to handle the hw_desc array correctly.

Additionally I propose to remove the axi_chan_start_first_queued() call after completing
the transfer, since it was identified that unbalance can occur (started descriptors can
be interrupted and transfer ignored due to DMA channel not being enabled).

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Link: https://lore.kernel.org/r/1711536564-12919-1-git-send-email-jpinto@synopsys.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
index a86a81ff0caa62e7467012a6a273325f5efad5dd..321446fdddbd7c8245c15a88d3bb072efbd3571a 100644 (file)
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -302,6 +302,7 @@ static struct axi_dma_desc *axi_desc_alloc(u32 num)
                kfree(desc);
                return NULL;
        }
+       desc->nr_hw_descs = num;
 
        return desc;
 }
@@ -328,7 +329,7 @@ static struct axi_dma_lli *axi_desc_get(struct axi_dma_chan *chan,
 static void axi_desc_put(struct axi_dma_desc *desc)
 {
        struct axi_dma_chan *chan = desc->chan;
-       int count = atomic_read(&chan->descs_allocated);
+       int count = desc->nr_hw_descs;
        struct axi_dma_hw_desc *hw_desc;
        int descs_put;
 
@@ -1139,9 +1140,6 @@ static void axi_chan_block_xfer_complete(struct axi_dma_chan *chan)
                /* Remove the completed descriptor from issued list before completing */
                list_del(&vd->node);
                vchan_cookie_complete(vd);
-
-               /* Submit queued descriptors after processing the completed ones */
-               axi_chan_start_first_queued(chan);
        }
 
 out:

diff --git a/drivers/dma/dw-axi-dmac/dw-axi-dmac.h b/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
index 454904d996540c4725c19b93b67f5d0ef8fb6f7c..ac571b413b21ccbcc53bec28db9a16d3d0dd5a37 100644 (file)
--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac.h
@@ -104,6 +104,7 @@ struct axi_dma_desc {
        u32                             completed_blocks;
        u32                             length;
        u32                             period_len;
+       u32                             nr_hw_descs;
 };
 
 struct axi_dma_chan_config {