Using ieee802154_subif_start_xmit() to bypass the net queue when
sending beacons is broken because it does not acquire the
HARD_TX_LOCK(), hence not preventing datagram buffers to be smashed by
beacons upon contention situation. Using the mlme_tx helper is not the
best fit either but at least it is not buggy and has little-to-no
performance hit. More details are given in the comment explaining this
choice in the code.
Fixes: 18fa625292e9 ("mac802154: Handle basic beaconing")
Reported-by: Alexander Aring <aahringo@xxxxxxxxxx>
Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
---
net/mac802154/scan.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/net/mac802154/scan.c b/net/mac802154/scan.c
index 8f98efec7753..fff41e59099e 100644
--- a/net/mac802154/scan.c
+++ b/net/mac802154/scan.c
@@ -326,7 +326,25 @@ static int mac802154_transmit_beacon(struct ieee802154_local *local,
return ret;
}
- return ieee802154_subif_start_xmit(skb, sdata->dev);
+ /* Using the MLME transmission helper for sending beacons is a bit
+ * overkill because we do not really care about the final outcome.
+ *
+ * Even though, going through the whole net stack with a regular
+ * dev_queue_xmit() is not relevant either because we want beacons to be
+ * sent "now" rather than go through the whole net stack scheduling
+ * (qdisc & co).
+ *
+ * Finally, using ieee802154_subif_start_xmit() would only be an option
+ * if we had a generic transmit helper which would acquire the
+ * HARD_TX_LOCK() to prevent buffer handling conflicts with regular
+ * packets.
+ *
+ * So for now we keep it simple and send beacons with our MLME helper,
+ * even if it stops the ieee802154 queue entirely during these
+ * transmissions, wich anyway does not have a huge impact on the
+ * performances given the current design of the stack.
+ */
+ return ieee802154_mlme_tx(local, sdata, skb);
}
void mac802154_beacon_worker(struct work_struct *work)
--
2.34.1
