On Sunday, March 27, 2011 09:52:57 pm Matt Evans wrote:
> On weakly-ordered systems, the reading of an event's content must occur
> after reading the event's validity.
>
> Signed-off-by: Matt Evans <matt@xxxxxxxxxx>
> ---
> Segher, thanks for the comment; explanation added.
>
> drivers/usb/host/xhci-ring.c | 5 +++++
> 1 files changed, 5 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index 45f3b77..d6aa880 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -2152,6 +2152,11 @@ static void xhci_handle_event(struct xhci_hcd
> *xhci) }
> xhci_dbg(xhci, "%s - OS owns TRB\n", __func__);
>
> + /*
> + * Barrier between reading the TRB_CYCLE (valid) flag above and any
> + * speculative reads of the event's flags/data below.
> + */
> + rmb();
> /* FIXME: Handle more event types. */
> switch ((le32_to_cpu(event->event_cmd.flags) & TRB_TYPE_BITMASK)) {
Isn't it the same memory that is being read the first time around? How
reordering could happen here?
Thanks.
--
Dmitry
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