On 03/02/2015 11:03 PM, Robert Jarzmik wrote:
Lars-Peter Clausen <lars@xxxxxxxxxx> writes:
On 03/02/2015 10:19 PM, Robert Jarzmik wrote:
diff --git a/drivers/dma/virt-dma.h b/drivers/dma/virt-dma.h
index 3772032..2a3da22 100644
--- a/drivers/dma/virt-dma.h
+++ b/drivers/dma/virt-dma.h
@@ -91,7 +91,7 @@ static inline void vchan_cookie_complete(struct virt_dma_desc *vd)
dma_cookie_complete(&vd->tx);
dev_vdbg(vc->chan.device->dev, "txd %p[%x]: marked complete\n",
vd, cookie);
- list_add_tail(&vd->node, &vc->desc_completed);
+ list_move_tail(&vd->node, &vc->desc_completed);
That will break all drivers which handle this currently correctly and remove the
descriptor from any list before calling vchan_cookie_complete.
Ah, well well I don't agree.
First, let's split the drivers which remove the descriptors and these which
don't :
These which remove the descriptor:
dma-jz4740.c
fsl-edma.c
These which don't remove the descriptor:
amba-pl08x.c
edma.c
img-mdc-dma.c
k3dma.c
moxart-dma.c
omap-dma.c
qcom_bam_dma.c
s3c24xx-dma.c
sa11x0-dma.c
sun6i-dma.c
All of those remove the descriptor from the list when they start the transfer.
That settles the correctness I think, the correct behavior is to not remove the
descriptor and let it be done by vchan_cookie_complete().
Now for the remaining 2 drivers, we'll have :
- list_del(&vd->node) => vd becomes a singleton
- list_move_tail(&vd->node, &...desc_completed)
=> list_del(&vd->node) : nothing changes, it's a nop
=> list_add_tail(&vd->node, &...desc_completed)
And the behavior remains correct after the patch, only one "list_del()" is done
twice for nothing. Where do you see any breakage ?
Calling list_del() on a list item that is not on a list causes undefined
behavior, which can result in memory corruption, segfaults, etc...
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