[PATCH net v6 3/4] tg3: Move tx queue stop logic to its own function

Benjamin Poirier
2014-09-05T01:31:34Z

It is duplicated. Also, the first instance in tg3_start_xmit() is racy.
Consider:

tg3_start_xmit()
if budget <= ...
tg3_tx()
(free up the entire ring)
tx_cons =
smp_mb
if queue_stopped and tx_avail, NO
if !queue_stopped
stop queue
return NETDEV_TX_BUSY

... tx queue stopped forever

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>

---

Changes v2->v3
* new patch to avoid repeatedly open coding this block in the next patch.

Changes v3->v4
* added a comment to clarify the return value, as suggested
* replaced the BUG_ON with netdev_err(). No need to be so dramatic, this
situation will trigger a netdev watchdog anyways.
---
drivers/net/ethernet/broadcom/tg3.c | 75 ++++++++++++++++++++-----------------
1 file changed, 40 insertions(+), 35 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index c5061c3..6e6b07c 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -7831,6 +7831,35 @@ static int tigon3_dma_hwbug_workaround(struct tg3_napi *tnapi,

static netdev_tx_t tg3_start_xmit(struct sk_buff *, struct net_device *);

+/* Returns true if the queue has been stopped. Note that it may have been
+ * restarted since.
+ */
+static inline bool tg3_maybe_stop_txq(struct tg3_napi *tnapi,
+ struct netdev_queue *txq,
+ u32 stop_thresh, u32 wakeup_thresh)
+{
+ bool stopped = false;
+
+ if (unlikely(tg3_tx_avail(tnapi) <= stop_thresh)) {
+ if (!netif_tx_queue_stopped(txq)) {
+ stopped = true;
+ netif_tx_stop_queue(txq);
+ if (wakeup_thresh >= tnapi->tx_pending)
+ netdev_err(tnapi->tp->dev,
+ "BUG! wakeup_thresh too large (%u >= %u)\n",
+ wakeup_thresh, tnapi->tx_pending);
+ }
+ /* netif_tx_stop_queue() must be done before checking tx index
+ * in tg3_tx_avail(), because in tg3_tx(), we update tx index
+ * before checking for netif_tx_queue_stopped().
+ */
+ smp_mb();
+ if (tg3_tx_avail(tnapi) > wakeup_thresh)
+ netif_tx_wake_queue(txq);
+ }
+ return stopped;
+}
+
/* Use GSO to workaround all TSO packets that meet HW bug conditions
* indicated in tg3_tx_frag_set()
*/
@@ -7841,20 +7870,9 @@ static int tg3_tso_bug(struct tg3 *tp, struct tg3_napi *tnapi,
u32 frag_cnt_est = skb_shinfo(skb)->gso_segs * 3;

/* Estimate the number of fragments in the worst case */
- if (unlikely(tg3_tx_avail(tnapi) <= frag_cnt_est)) {
- netif_tx_stop_queue(txq);
-
- /* netif_tx_stop_queue() must be done before checking
- * checking tx index in tg3_tx_avail() below, because in
- * tg3_tx(), we update tx index before checking for
- * netif_tx_queue_stopped().
- */
- smp_mb();
- if (tg3_tx_avail(tnapi) <= frag_cnt_est)
- return NETDEV_TX_BUSY;
-
- netif_tx_wake_queue(txq);
- }
+ tg3_maybe_stop_txq(tnapi, txq, frag_cnt_est, frag_cnt_est);
+ if (netif_tx_queue_stopped(txq))
+ return NETDEV_TX_BUSY;

segs = skb_gso_segment(skb, tp->dev->features &
~(NETIF_F_TSO | NETIF_F_TSO6));
@@ -7902,16 +7920,13 @@ static netdev_tx_t tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
* interrupt. Furthermore, IRQ processing runs lockless so we have
* no IRQ context deadlocks to worry about either. Rejoice!
*/
- if (unlikely(budget <= (skb_shinfo(skb)->nr_frags + 1))) {
- if (!netif_tx_queue_stopped(txq)) {
- netif_tx_stop_queue(txq);
-
- /* This is a hard error, log it. */
- netdev_err(dev,
- "BUG! Tx Ring full when queue awake!\n");
- }
- return NETDEV_TX_BUSY;
+ if (tg3_maybe_stop_txq(tnapi, txq, skb_shinfo(skb)->nr_frags + 1,
+ TG3_TX_WAKEUP_THRESH(tnapi))) {
+ /* This is a hard error, log it. */
+ netdev_err(dev, "BUG! Tx Ring full when queue awake!\n");
}
+ if (netif_tx_queue_stopped(txq))
+ return NETDEV_TX_BUSY;

entry = tnapi->tx_prod;
base_flags = 0;
@@ -8087,18 +8102,8 @@ static netdev_tx_t tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
tw32_tx_mbox(tnapi->prodmbox, entry);

tnapi->tx_prod = entry;
- if (unlikely(tg3_tx_avail(tnapi) <= (MAX_SKB_FRAGS + 1))) {
- netif_tx_stop_queue(txq);
-
- /* netif_tx_stop_queue() must be done before checking
- * checking tx index in tg3_tx_avail() below, because in
- * tg3_tx(), we update tx index before checking for
- * netif_tx_queue_stopped().
- */
- smp_mb();
- if (tg3_tx_avail(tnapi) > TG3_TX_WAKEUP_THRESH(tnapi))
- netif_tx_wake_queue(txq);
- }
+ tg3_maybe_stop_txq(tnapi, txq, MAX_SKB_FRAGS + 1,
+ TG3_TX_WAKEUP_THRESH(tnapi));

mmiowb();
return NETDEV_TX_OK;
--
1.8.4.5