Messages in this thread | | | From | Radhey Shyam Pandey <> | Subject | RE: [PATCH 03/14] net: axienet: Fix DMA descriptor cleanup path | Date | Fri, 10 Jan 2020 17:05:45 +0000 |
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> -----Original Message----- > From: Andre Przywara <andre.przywara@arm.com> > Sent: Friday, January 10, 2020 9:13 PM > To: Radhey Shyam Pandey <radheys@xilinx.com> > Cc: David S . Miller <davem@davemloft.net>; Michal Simek > <michals@xilinx.com>; Robert Hancock <hancock@sedsystems.ca>; > netdev@vger.kernel.org; linux-arm-kernel@lists.infradead.org; linux- > kernel@vger.kernel.org > Subject: Re: [PATCH 03/14] net: axienet: Fix DMA descriptor cleanup path > > On Fri, 10 Jan 2020 15:14:46 +0000 > Radhey Shyam Pandey <radheys@xilinx.com> wrote: > > Hi Radhey, > > thanks for having a look! > > > > -----Original Message----- > > > From: Andre Przywara <andre.przywara@arm.com> > > > Sent: Friday, January 10, 2020 5:24 PM > > > To: David S . Miller <davem@davemloft.net>; Radhey Shyam Pandey > > > <radheys@xilinx.com> > > > Cc: Michal Simek <michals@xilinx.com>; Robert Hancock > > > <hancock@sedsystems.ca>; netdev@vger.kernel.org; linux-arm- > > > kernel@lists.infradead.org; linux-kernel@vger.kernel.org > > > Subject: [PATCH 03/14] net: axienet: Fix DMA descriptor cleanup path > > > > > > When axienet_dma_bd_init() bails out during the initialisation process, > > > it might do so with parts of the structure already allocated and > > > initialised, while other parts have not been touched yet. Before > > > returning in this case, we call axienet_dma_bd_release(), which does not > > > take care of this corner case. > > > This is most obvious by the first loop happily dereferencing > > > lp->rx_bd_v, which we actually check to be non NULL *afterwards*. > > > > > > Make sure we only unmap or free already allocated structures, by: > > > - directly returning with -ENOMEM if nothing has been allocated at all > > > - checking for lp->rx_bd_v to be non-NULL *before* using it > > > - only unmapping allocated DMA RX regions > > > > > > This avoids NULL pointer dereferences when initialisation fails. > > > > > > Signed-off-by: Andre Przywara <andre.przywara@arm.com> > > > --- > > > .../net/ethernet/xilinx/xilinx_axienet_main.c | 43 ++++++++++++------- > > > 1 file changed, 28 insertions(+), 15 deletions(-) > > > > > > diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c > > > b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c > > > index 97482cf093ce..7e90044cf2d9 100644 > > > --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c > > > +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c > > > @@ -160,24 +160,37 @@ static void axienet_dma_bd_release(struct > > > net_device *ndev) > > > int i; > > > struct axienet_local *lp = netdev_priv(ndev); > > > > > > + /* If we end up here, tx_bd_v must have been DMA allocated. */ > > > + dma_free_coherent(ndev->dev.parent, > > > + sizeof(*lp->tx_bd_v) * lp->tx_bd_num, > > > + lp->tx_bd_v, > > > + lp->tx_bd_p); > > > + > > > + if (!lp->rx_bd_v) > > > + return; > > > + > > > for (i = 0; i < lp->rx_bd_num; i++) { > > > - dma_unmap_single(ndev->dev.parent, lp->rx_bd_v[i].phys, > > > - lp->max_frm_size, DMA_FROM_DEVICE); > > > + /* A NULL skb means this descriptor has not been initialised > > > + * at all. > > > + */ > > > + if (!lp->rx_bd_v[i].skb) > > > + break; > > > + > > > dev_kfree_skb(lp->rx_bd_v[i].skb); > > > - } > > > > > > - if (lp->rx_bd_v) { > > > - dma_free_coherent(ndev->dev.parent, > > > - sizeof(*lp->rx_bd_v) * lp->rx_bd_num, > > > - lp->rx_bd_v, > > > - lp->rx_bd_p); > > > - } > > > - if (lp->tx_bd_v) { > > > - dma_free_coherent(ndev->dev.parent, > > > - sizeof(*lp->tx_bd_v) * lp->tx_bd_num, > > > - lp->tx_bd_v, > > > - lp->tx_bd_p); > > > + /* For each descriptor, we programmed cntrl with the (non- > > > zero) > > > + * descriptor size, after it had been successfully allocated. > > > + * So a non-zero value in there means we need to unmap it. > > > + */ > > > > > + if (lp->rx_bd_v[i].cntrl) > > > > I think it should ok to unmap w/o any check? > > Do you mean because .phys would be 0 if not initialised? AFAIK 0 can be a > valid DMA address, so there is no special check for that, and unmapping > DMA address 0 will probably go wrong at some point. So it's unlike > kfree(NULL).
I mean if skb allocation is successful in _dma_bd_init then in release path we can assume .phys is always a valid address and skip rx_bd_v[i].cntrl check. > > Cheers, > Andre. > > > > > + dma_unmap_single(ndev->dev.parent, lp- > > > >rx_bd_v[i].phys, > > > + lp->max_frm_size, > > > DMA_FROM_DEVICE); > > > } > > > + > > > + dma_free_coherent(ndev->dev.parent, > > > + sizeof(*lp->rx_bd_v) * lp->rx_bd_num, > > > + lp->rx_bd_v, > > > + lp->rx_bd_p); > > > } > > > > > > /** > > > @@ -207,7 +220,7 @@ static int axienet_dma_bd_init(struct net_device > > > *ndev) > > > sizeof(*lp->tx_bd_v) * lp- > > > >tx_bd_num, > > > &lp->tx_bd_p, GFP_KERNEL); > > > if (!lp->tx_bd_v) > > > - goto out; > > > + return -ENOMEM; > > > > > > lp->rx_bd_v = dma_alloc_coherent(ndev->dev.parent, > > > sizeof(*lp->rx_bd_v) * lp- > > > >rx_bd_num, > > > -- > > > 2.17.1 > >
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