Dan Carpenter reported that smatch detected a potential
problem with the code [1]:
drivers/net/wireless/ath/carl9170/tx.c:1488 carl9170_op_tx()
error: we previously assumed 'sta' could be null (see line 1482)
drivers/net/wireless/ath/carl9170/tx.c
1482 if (sta) {
^^^^^ New check.
[...]
1485 }
1487 if (info->flags & IEEE80211_TX_CTL_AMPDU) {
1488 run = carl9170_tx_ampdu_queue(ar, sta, skb);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Old dereference of "sta" inside the call to carl9170_tx_ampdu_queue().
A range of solutions have been discussed in [2] and
we agreed on the following: "
> we might as well add a comment to carl9170_tx_ampdu_queue
> and explain the situation [in a way that's obvious to a
> human reader]. This way we can save the "if"... which is
> a small win since carl9170_op_tx is sort of a hot-path.
Putting a comment there is fine. Without the comment
it's easy for a human reader to get confused why the
check is there. So long as humans can read the code,
that's all that matters."
[1] <http://www.spinics.net/lists/linux-wireless/msg94526.html>
[2] <http://www.spinics.net/lists/linux-kernel-janitors/msg14953.html>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Christian Lamparter <chunkeey@xxxxxxxxxxxxxx>
---
drivers/net/wireless/ath/carl9170/tx.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/net/wireless/ath/carl9170/tx.c b/drivers/net/wireless/ath/carl9170/tx.c
index 6a86814..45c696b 100644
--- a/drivers/net/wireless/ath/carl9170/tx.c
+++ b/drivers/net/wireless/ath/carl9170/tx.c
@@ -1485,6 +1485,13 @@ void carl9170_op_tx(struct ieee80211_hw *hw, struct sk_buff *skb)
}
if (info->flags & IEEE80211_TX_CTL_AMPDU) {
+ /* to static code analyzers and reviewers:
+ * mac80211 guarantees that a valid "sta"
+ * reference is present, if a frame is to
+ * be part of an ampdu. Hence any extra
+ * sta == NULL checks are redundant in this
+ * special case.
+ */
run = carl9170_tx_ampdu_queue(ar, sta, skb);
if (run)
carl9170_tx_ampdu(ar);
--
1.7.10.4
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