On Friday 14 August 2009 04:01:35 Luis R. Rodriguez wrote:
> If someone pulls the harware out while RX'ing a lot of traffic
> I would funky data may be passed, BUG_ON() seems pretty extreme
> so lets just drop the frame as we do when the length does not
> meet our criteria for processing.
>
> Cc: Christian Lamparter <chunkeey@xxxxxx>
> Signed-off-by: Luis R. Rodriguez <lrodriguez@xxxxxxxxxxx>
> ---
>
> This one depends on my previous patch.
>
> drivers/net/wireless/ath/ar9170/main.c | 7 +++++--
> 1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ar9170/main.c b/drivers/net/wireless/ath/ar9170/main.c
> index 75c317d..0bbbc36 100644
> --- a/drivers/net/wireless/ath/ar9170/main.c
> +++ b/drivers/net/wireless/ath/ar9170/main.c
> @@ -1068,8 +1068,11 @@ static void ar9170_handle_mpdu(struct ar9170 *ar, u8 *buf, int len)
> break;
>
> default:
> - BUG_ON(1);
> - break;
> + if (ar9170_nag_limiter(ar))
> + printk(KERN_ERR "%s: rx'd unexpected "
> + "type of MPDU.\n",
> + wiphy_name(ar->hw->wiphy));
> + return;
> }
no, this is really impossible! really!
But let's take a closer look why should be so:
the switch goes like this:
> switch (mac->status & AR9170_RX_STATUS_MPDU_MASK) {
mac->status is a u8 and AND with AR9170_RX_STATUS_MPDU_MASK.
AR9170_RX_STATUS_MPDU_MASK (etc.) is #define in hw.h
and it's a 0x30 _mask_.
This leaves only four possibilities: 0x00, 0x10, 0x20, 0x30.
>case AR9170_RX_STATUS_MPDU_FIRST: (case 0x20:)
>case AR9170_RX_STATUS_MPDU_LAST: (case 0x10:)
>case AR9170_RX_STATUS_MPDU_MIDDLE: (case 0x30:)
>case AR9170_RX_STATUS_MPDU_SINGLE: (case 0x00:)
so the default case is a deadly dead code path here ;-).
And the reason why you see it was because some checker tool kept
complaining about unlikely _corner_ cases.
> if (unlikely(mpdu_len < FCS_LEN))
Regards,
Chr
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