From 2f8af120a159a843948749ea88bcacda9779b132 Mon Sep 17 00:00:00 2001 From: Michael Chan Date: Tue, 15 Aug 2006 01:39:10 -0700 Subject: [BNX2]: Fix tx race condition. Fix a subtle race condition between bnx2_start_xmit() and bnx2_tx_int() similar to the one in tg3 discovered by Herbert Xu: CPU0 CPU1 bnx2_start_xmit() if (tx_ring_full) { tx_lock bnx2_tx() if (!netif_queue_stopped) netif_stop_queue() if (!tx_ring_full) update_tx_ring netif_wake_queue() tx_unlock } Even though tx_ring is updated before the if statement in bnx2_tx_int() in program order, it can be re-ordered by the CPU as shown above. This scenario can cause the tx queue to be stopped forever if bnx2_tx_int() has just freed up the entire tx_ring. The possibility of this happening should be very rare though. The following changes are made, very much identical to the tg3 fix: 1. Add memory barrier to fix the above race condition. 2. Eliminate the private tx_lock altogether and rely solely on netif_tx_lock. This eliminates one spinlock in bnx2_start_xmit() when the ring is full. 3. Because of 2, use netif_tx_lock in bnx2_tx_int() before calling netif_wake_queue(). 4. Add memory barrier to bnx2_tx_avail(). 5. Add bp->tx_wake_thresh which is set to half the tx ring size. 6. Check for the full wake queue condition before getting netif_tx_lock in tg3_tx(). This reduces the number of unnecessary spinlocks when the tx ring is full in a steady-state condition. Signed-off-by: Michael Chan Signed-off-by: David S. Miller --- drivers/net/bnx2.c | 35 +++++++++++++++++++---------------- drivers/net/bnx2.h | 12 +++++------- 2 files changed, 24 insertions(+), 23 deletions(-) (limited to 'drivers') diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c index db73de0d2511..2099edbbfdfd 100644 --- a/drivers/net/bnx2.c +++ b/drivers/net/bnx2.c @@ -209,8 +209,10 @@ MODULE_DEVICE_TABLE(pci, bnx2_pci_tbl); static inline u32 bnx2_tx_avail(struct bnx2 *bp) { - u32 diff = TX_RING_IDX(bp->tx_prod) - TX_RING_IDX(bp->tx_cons); + u32 diff; + smp_mb(); + diff = TX_RING_IDX(bp->tx_prod) - TX_RING_IDX(bp->tx_cons); if (diff > MAX_TX_DESC_CNT) diff = (diff & MAX_TX_DESC_CNT) - 1; return (bp->tx_ring_size - diff); @@ -1686,15 +1688,20 @@ bnx2_tx_int(struct bnx2 *bp) } bp->tx_cons = sw_cons; + /* Need to make the tx_cons update visible to bnx2_start_xmit() + * before checking for netif_queue_stopped(). Without the + * memory barrier, there is a small possibility that bnx2_start_xmit() + * will miss it and cause the queue to be stopped forever. + */ + smp_mb(); - if (unlikely(netif_queue_stopped(bp->dev))) { - spin_lock(&bp->tx_lock); + if (unlikely(netif_queue_stopped(bp->dev)) && + (bnx2_tx_avail(bp) > bp->tx_wake_thresh)) { + netif_tx_lock(bp->dev); if ((netif_queue_stopped(bp->dev)) && - (bnx2_tx_avail(bp) > MAX_SKB_FRAGS)) { - + (bnx2_tx_avail(bp) > bp->tx_wake_thresh)) netif_wake_queue(bp->dev); - } - spin_unlock(&bp->tx_lock); + netif_tx_unlock(bp->dev); } } @@ -3503,6 +3510,8 @@ bnx2_init_tx_ring(struct bnx2 *bp) struct tx_bd *txbd; u32 val; + bp->tx_wake_thresh = bp->tx_ring_size / 2; + txbd = &bp->tx_desc_ring[MAX_TX_DESC_CNT]; txbd->tx_bd_haddr_hi = (u64) bp->tx_desc_mapping >> 32; @@ -4390,10 +4399,8 @@ bnx2_vlan_rx_kill_vid(struct net_device *dev, uint16_t vid) #endif /* Called with netif_tx_lock. - * hard_start_xmit is pseudo-lockless - a lock is only required when - * the tx queue is full. This way, we get the benefit of lockless - * operations most of the time without the complexities to handle - * netif_stop_queue/wake_queue race conditions. + * bnx2_tx_int() runs without netif_tx_lock unless it needs to call + * netif_wake_queue(). */ static int bnx2_start_xmit(struct sk_buff *skb, struct net_device *dev) @@ -4512,12 +4519,9 @@ bnx2_start_xmit(struct sk_buff *skb, struct net_device *dev) dev->trans_start = jiffies; if (unlikely(bnx2_tx_avail(bp) <= MAX_SKB_FRAGS)) { - spin_lock(&bp->tx_lock); netif_stop_queue(dev); - - if (bnx2_tx_avail(bp) > MAX_SKB_FRAGS) + if (bnx2_tx_avail(bp) > bp->tx_wake_thresh) netif_wake_queue(dev); - spin_unlock(&bp->tx_lock); } return NETDEV_TX_OK; @@ -5628,7 +5632,6 @@ bnx2_init_board(struct pci_dev *pdev, struct net_device *dev) bp->pdev = pdev; spin_lock_init(&bp->phy_lock); - spin_lock_init(&bp->tx_lock); INIT_WORK(&bp->reset_task, bnx2_reset_task, bp); dev->base_addr = dev->mem_start = pci_resource_start(pdev, 0); diff --git a/drivers/net/bnx2.h b/drivers/net/bnx2.h index 658c5ee95c73..fe804763c607 100644 --- a/drivers/net/bnx2.h +++ b/drivers/net/bnx2.h @@ -3890,10 +3890,6 @@ struct bnx2 { u32 tx_prod_bseq __attribute__((aligned(L1_CACHE_BYTES))); u16 tx_prod; - struct tx_bd *tx_desc_ring; - struct sw_bd *tx_buf_ring; - int tx_ring_size; - u16 tx_cons __attribute__((aligned(L1_CACHE_BYTES))); u16 hw_tx_cons; @@ -3916,9 +3912,11 @@ struct bnx2 { struct sw_bd *rx_buf_ring; struct rx_bd *rx_desc_ring[MAX_RX_RINGS]; - /* Only used to synchronize netif_stop_queue/wake_queue when tx */ - /* ring is full */ - spinlock_t tx_lock; + /* TX constants */ + struct tx_bd *tx_desc_ring; + struct sw_bd *tx_buf_ring; + int tx_ring_size; + u32 tx_wake_thresh; /* End of fields used in the performance code paths. */ -- cgit v1.2.2