| Message ID | 1397782610-7370-1-git-send-email-joelf@ti.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Apr 17, 2014 at 07:56:50PM -0500, Joel Fernandes wrote: > 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.
On 04/18/2014 03:50 AM, Russell King - ARM Linux wrote: > On Thu, Apr 17, 2014 at 07:56:50PM -0500, Joel Fernandes wrote: >> 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
On Fri, Apr 18, 2014 at 11:34:50AM -0500, Joel Fernandes wrote: > On 04/18/2014 03:50 AM, Russell King - ARM Linux wrote: > > On Thu, Apr 17, 2014 at 07:56:50PM -0500, Joel Fernandes wrote: > >> 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
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); } }
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@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Joel Fernandes <joelf@ti.com> --- drivers/dma/virt-dma.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)