[PATCH] [FIX] dmaengine: virt-dma: Free descriptor after callback

[Joel Fernandes]

Free the vd (virt descriptor) after the callback is called. In EDMA driver
atleast which uses virt-dma, we make use of the desc during the callback and if
its dangerously freed before the callback is called. I also noticed this in
omap-dma dmaengine driver.

Cc: Vinod Koul <vinod.koul at intel.com>
Cc: Dan Williams <dan.j.williams at intel.com>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
Signed-off-by: Joel Fernandes <joelf at ti.com>
---
drivers/dma/virt-dma.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/virt-dma.c b/drivers/dma/virt-dma.c
index 6f80432..98aeb7f 100644
--- a/drivers/dma/virt-dma.c
+++ b/drivers/dma/virt-dma.c
@@ -84,10 +84,10 @@ static void vchan_complete(unsigned long arg)

list_del(&vd->node);

- vc->desc_free(vd);
-
if (cb)
cb(cb_data);
+
+ vc->desc_free(vd);
}
}

[Russell King - ARM Linux]

Post by Joel Fernandes
Free the vd (virt descriptor) after the callback is called. In EDMA driver
atleast which uses virt-dma, we make use of the desc during the callback and if
its dangerously freed before the callback is called. I also noticed this in
omap-dma dmaengine driver.

You've missed the vital bit of information: why do you make use of the
descriptor afterwards? You shouldn't. omap-dma doesn't either.

Once clients submit their request to DMA engine, they must not hold any
kind of reference to the descriptor other than the cookie.

[Joel Fernandes]

Post by Russell King - ARM Linux

Post by Joel Fernandes
Free the vd (virt descriptor) after the callback is called. In EDMA driver
atleast which uses virt-dma, we make use of the desc during the callback and if
its dangerously freed before the callback is called. I also noticed this in
omap-dma dmaengine driver.

You've missed the vital bit of information: why do you make use of the
descriptor afterwards? You shouldn't. omap-dma doesn't either.
Once clients submit their request to DMA engine, they must not hold any
kind of reference to the descriptor other than the cookie.

Sorry, I confused edma/omap-dma callbacks for virt dma callbacks.

Anyway, I think there is still a chance in edma that we refer to the
echan->edesc pointer later on after virt-dma calls the free (in
edma_execute), so I'll just NULL that out to be safe and submit a patch.
Thanks.

regards,
-Joel

[Vinod Koul]

Post by Joel Fernandes

Post by Russell King - ARM Linux

Post by Joel Fernandes
Free the vd (virt descriptor) after the callback is called. In EDMA driver
atleast which uses virt-dma, we make use of the desc during the callback and if
its dangerously freed before the callback is called. I also noticed this in
omap-dma dmaengine driver.

You've missed the vital bit of information: why do you make use of the
descriptor afterwards? You shouldn't. omap-dma doesn't either.
Once clients submit their request to DMA engine, they must not hold any
kind of reference to the descriptor other than the cookie.

Sorry, I confused edma/omap-dma callbacks for virt dma callbacks.
Anyway, I think there is still a chance in edma that we refer to the
echan->edesc pointer later on after virt-dma calls the free (in
edma_execute), so I'll just NULL that out to be safe and submit a patch.

Yes, that would be the right way :)

While looking at this, I see it is not called out specfically in documentation, will update
that as well