carl9170: remove unneeded NULL check

Commit Message

Christian Lamparter Dec. 2, 2012, 1:49 p.m. UTC

On Sunday 02 December 2012 11:42:38 Dan Carpenter wrote:
> The "sta" variable is not checked for NULL consistently and it makes the
> static checkers complain.  I asked Christian Lamparter about this and
> it turns out the check is not needed.  "In fact, in order to set up a
> ampdu session, the stack would call the driver's op_ampdu_action
> callback which always needs a station."

that would be from the thread:
<http://www.spinics.net/lists/linux-wireless/msg94526.html>
 
> I have removed the check.
I think this will bug for multicast and injected frames.
 
It is not possible for the sta(tion) pointer to be NULL if
the frame has the IEEE80211_TX_CTL_AMPDU flag set. So the
sta == NULL check can be avoided when calling 
carl9170_tx_ampdu_queue. This is because mac80211 tracks
all aggregation sessions within the station struct.
Of course, this is something that the checker tool can't
possibly deduce, but it has a point and we can add a check
like this [see attached draft patch]:

What do you think [or more to the point: what does the
checker say?]

Regards,
	Chr
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Comments

Dan Carpenter Dec. 2, 2012, 4:51 p.m. UTC | #1

On Sun, Dec 02, 2012 at 02:49:20PM +0100, Christian Lamparter wrote:
> On Sunday 02 December 2012 11:42:38 Dan Carpenter wrote:
> > The "sta" variable is not checked for NULL consistently and it makes the
> > static checkers complain.  I asked Christian Lamparter about this and
> > it turns out the check is not needed.  "In fact, in order to set up a
> > ampdu session, the stack would call the driver's op_ampdu_action
> > callback which always needs a station."
> 
> that would be from the thread:
> <http://www.spinics.net/lists/linux-wireless/msg94526.html>
>  
> > I have removed the check.
> I think this will bug for multicast and injected frames.
>  
> It is not possible for the sta(tion) pointer to be NULL if
> the frame has the IEEE80211_TX_CTL_AMPDU flag set. So the
> sta == NULL check can be avoided when calling 
> carl9170_tx_ampdu_queue. This is because mac80211 tracks
> all aggregation sessions within the station struct.
> Of course, this is something that the checker tool can't
> possibly deduce, but it has a point and we can add a check
> like this [see attached draft patch]:
> 
> What do you think [or more to the point: what does the
> checker say?]
> 

So we wouldn't apply my patch, we would apply that one instead?

I think that's great.  My static checker doesn't understand bit
flags yet so it would complain but it would be obvious to a human
reader.

Could you just resend that patch with a signed-off-by?

regards,
dan carpenter

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Patch

diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 84377cf..e09d293 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -1470,6 +1470,9 @@  void carl9170_op_tx(struct ieee80211_hw *hw,
 
 	info = IEEE80211_SKB_CB(skb);
 
+	if ((info->flags & IEEE80211_TX_CTL_AMPDU) && WARN_ON_ONCE(!sta))
+		goto err_free;
+
 	if (unlikely(carl9170_tx_prepare(ar, sta, skb)))
 		goto err_free;