On Sat, 24 Jan 2015, Alexey Khoroshilov wrote:
> oxu_qh_alloc() acquires oxu->mem_lock spinlock, finds free qh slot
> and calls ehci_qtd_alloc() to initialize qh->dummy, but
> ehci_qtd_alloc() acquires oxu->mem_lock as well.
> That means an unavoidable deadlock in oxu_qh_alloc().
>
> The patch fixes the issue by introduction of unlocked version
> of ehci_qtd_alloc().
This deadlock would affect anybody the moment they plugged a USB device
into one of these controllers, right?
Which means nobody can possibly be using them under Linux. So wouldn't
it be better to remove the driver entirely?
Alan Stern
> Found by Linux Driver Verification project (linuxtesting.org).
>
> Signed-off-by: Alexey Khoroshilov <khoroshilov@xxxxxxxxx>
> ---
> drivers/usb/host/oxu210hp-hcd.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/host/oxu210hp-hcd.c b/drivers/usb/host/oxu210hp-hcd.c
> index 036924e640f5..15d4cf2c35cd 100644
> --- a/drivers/usb/host/oxu210hp-hcd.c
> +++ b/drivers/usb/host/oxu210hp-hcd.c
> @@ -573,13 +573,11 @@ static inline void oxu_qtd_free(struct oxu_hcd *oxu, struct ehci_qtd *qtd)
> spin_unlock(&oxu->mem_lock);
> }
>
> -static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
> +static struct ehci_qtd *ehci_qtd_alloc_unlocked(struct oxu_hcd *oxu)
> {
> int i;
> struct ehci_qtd *qtd = NULL;
>
> - spin_lock(&oxu->mem_lock);
> -
> for (i = 0; i < QTD_NUM; i++)
> if (!oxu->qtd_used[i])
> break;
> @@ -598,6 +596,17 @@ static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
> oxu->qtd_used[i] = 1;
> }
>
> + return qtd;
> +}
> +
> +static struct ehci_qtd *ehci_qtd_alloc(struct oxu_hcd *oxu)
> +{
> + struct ehci_qtd *qtd;
> +
> + spin_lock(&oxu->mem_lock);
> +
> + qtd = ehci_qtd_alloc_unlocked(oxu);
> +
> spin_unlock(&oxu->mem_lock);
>
> return qtd;
> @@ -651,7 +660,7 @@ static struct ehci_qh *oxu_qh_alloc(struct oxu_hcd *oxu)
> INIT_LIST_HEAD(&qh->qtd_list);
>
> /* dummy td enables safe urb queuing */
> - qh->dummy = ehci_qtd_alloc(oxu);
> + qh->dummy = ehci_qtd_alloc_unlocked(oxu);
> if (qh->dummy == NULL) {
> oxu_dbg(oxu, "no dummy td\n");
> oxu->qh_used[i] = 0;
>
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