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authorMichael Chan <mchan@broadcom.com>2006-08-15 01:39:10 -0700
committerDavid S. Miller <davem@sunset.davemloft.net>2006-08-17 16:29:51 -0700
commit2f8af120a159a843948749ea88bcacda9779b132 (patch)
treee633037a72db856b8078e814e3451dd8f44c14de
parentfb33f82568d32016b3b3c00819574f9526e52be3 (diff)
[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 <mchan@broadcom.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--drivers/net/bnx2.c35
-rw-r--r--drivers/net/bnx2.h12
2 files changed, 24 insertions, 23 deletions
diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c
index db73de0d251..2099edbbfdf 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 658c5ee95c7..fe804763c60 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. */