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From: Alan Stern on 28 Jun 2010 10:20
On Mon, 28 Jun 2010, Andrea Righi wrote:

> If we use the HCD_LOCAL_MEM flag and dma_declare_coherent_memory() to
> enforce the host controller's local memory utilization we also need to
> disable native scatter-gather support, otherwise hcd_alloc_coherent() in
> map_urb_for_dma() is called with urb->transfer_buffer == NULL, that
> triggers a NULL pointer dereference.
>
> We can also consider to add a WARN_ON() and return an error code to
> better catch this problem in the future.
>
> Signed-off-by: Andrea Righi <arighi(a)develer.com>
> ---
> drivers/usb/core/hcd.c | 5 +++++
> drivers/usb/host/ehci-hcd.c | 3 ++-
> 2 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 12742f1..161c757 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1219,6 +1219,11 @@ static int hcd_alloc_coherent(struct usb_bus *bus,
> {
> unsigned char *vaddr;
>
> + if (*vaddr_handle == NULL) {
> + WARN_ON_ONCE(1);
> + return -EFAULT;
> + }
> +
> vaddr = hcd_buffer_alloc(bus, size + sizeof(vaddr),
> mem_flags, dma_handle);
> if (!vaddr)
> diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> index a3ef2a9..27e0351 100644
> --- a/drivers/usb/host/ehci-hcd.c
> +++ b/drivers/usb/host/ehci-hcd.c
> @@ -606,7 +606,8 @@ static int ehci_init(struct usb_hcd *hcd)
> ehci->command = temp;
>
> /* Accept arbitrarily long scatter-gather lists */
> - hcd->self.sg_tablesize = ~0;
> + if (!(hcd->driver->flags & HCD_LOCAL_MEM))
> + hcd->self.sg_tablesize = ~0;
> return 0;
> }

Looks okay to me. You can add my Acked-by: when you submit this to
Greg KH.

Alan Stern

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