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authorMichael Chan <mchan@broadcom.com>2006-08-07 21:46:02 -0700
committerDavid S. Miller <davem@davemloft.net>2006-08-07 21:46:02 -0700
commit1b2a720506ccf7c30baaeda5d990c29b31e21726 (patch)
tree5990f56e364077c83563566ed64beae95b855a9f /drivers/net
parentbd37a088596ccdb2b2dd3299e25e333bca7a9a34 (diff)
[TG3]: Fix tx race condition
Fix a subtle race condition between tg3_start_xmit() and tg3_tx() discovered by Herbert Xu <herbert@gondor.apana.org.au>: CPU0 CPU1 tg3_start_xmit() if (tx_ring_full) { tx_lock tg3_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 tg3_tx() 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 tg3_tx() has just freed up the entire tx_ring. The possibility of this happening should be very rare though. The following changes are made: 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 tg3_start_xmit() when the ring is full. 3. Because of 2, use netif_tx_lock in tg3_tx() before calling netif_wake_queue(). 4. Change TX_BUFFS_AVAIL to an inline function with a memory barrier. Herbert and David suggested using the memory barrier instead of volatile. 5. 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. 6. Update version to 3.65. Signed-off-by: Michael Chan <mchan@broadcom.com> Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/net')
-rw-r--r--drivers/net/tg3.c49
-rw-r--r--drivers/net/tg3.h8
2 files changed, 31 insertions, 26 deletions
diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
index 0afbed6753f..eafabb253f0 100644
--- a/drivers/net/tg3.c
+++ b/drivers/net/tg3.c
@@ -68,8 +68,8 @@
#define DRV_MODULE_NAME "tg3"
#define PFX DRV_MODULE_NAME ": "
-#define DRV_MODULE_VERSION "3.64"
-#define DRV_MODULE_RELDATE "July 31, 2006"
+#define DRV_MODULE_VERSION "3.65"
+#define DRV_MODULE_RELDATE "August 07, 2006"
#define TG3_DEF_MAC_MODE 0
#define TG3_DEF_RX_MODE 0
@@ -123,9 +123,6 @@
TG3_RX_RCB_RING_SIZE(tp))
#define TG3_TX_RING_BYTES (sizeof(struct tg3_tx_buffer_desc) * \
TG3_TX_RING_SIZE)
-#define TX_BUFFS_AVAIL(TP) \
- ((TP)->tx_pending - \
- (((TP)->tx_prod - (TP)->tx_cons) & (TG3_TX_RING_SIZE - 1)))
#define NEXT_TX(N) (((N) + 1) & (TG3_TX_RING_SIZE - 1))
#define RX_PKT_BUF_SZ (1536 + tp->rx_offset + 64)
@@ -2987,6 +2984,13 @@ static void tg3_tx_recover(struct tg3 *tp)
spin_unlock(&tp->lock);
}
+static inline u32 tg3_tx_avail(struct tg3 *tp)
+{
+ smp_mb();
+ return (tp->tx_pending -
+ ((tp->tx_prod - tp->tx_cons) & (TG3_TX_RING_SIZE - 1)));
+}
+
/* Tigon3 never reports partial packet sends. So we do not
* need special logic to handle SKBs that have not had all
* of their frags sent yet, like SunGEM does.
@@ -3038,12 +3042,20 @@ static void tg3_tx(struct tg3 *tp)
tp->tx_cons = sw_idx;
- if (unlikely(netif_queue_stopped(tp->dev))) {
- spin_lock(&tp->tx_lock);
+ /* Need to make the tx_cons update visible to tg3_start_xmit()
+ * before checking for netif_queue_stopped(). Without the
+ * memory barrier, there is a small possibility that tg3_start_xmit()
+ * will miss it and cause the queue to be stopped forever.
+ */
+ smp_mb();
+
+ if (unlikely(netif_queue_stopped(tp->dev) &&
+ (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH))) {
+ netif_tx_lock(tp->dev);
if (netif_queue_stopped(tp->dev) &&
- (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH))
+ (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH))
netif_wake_queue(tp->dev);
- spin_unlock(&tp->tx_lock);
+ netif_tx_unlock(tp->dev);
}
}
@@ -3795,7 +3807,7 @@ static int 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(TX_BUFFS_AVAIL(tp) <= (skb_shinfo(skb)->nr_frags + 1))) {
+ if (unlikely(tg3_tx_avail(tp) <= (skb_shinfo(skb)->nr_frags + 1))) {
if (!netif_queue_stopped(dev)) {
netif_stop_queue(dev);
@@ -3891,12 +3903,10 @@ static int tg3_start_xmit(struct sk_buff *skb, struct net_device *dev)
tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);
tp->tx_prod = entry;
- if (unlikely(TX_BUFFS_AVAIL(tp) <= (MAX_SKB_FRAGS + 1))) {
- spin_lock(&tp->tx_lock);
+ if (unlikely(tg3_tx_avail(tp) <= (MAX_SKB_FRAGS + 1))) {
netif_stop_queue(dev);
- if (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH)
+ if (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH)
netif_wake_queue(tp->dev);
- spin_unlock(&tp->tx_lock);
}
out_unlock:
@@ -3918,7 +3928,7 @@ static int tg3_tso_bug(struct tg3 *tp, struct sk_buff *skb)
struct sk_buff *segs, *nskb;
/* Estimate the number of fragments in the worst case */
- if (unlikely(TX_BUFFS_AVAIL(tp) <= (skb_shinfo(skb)->gso_segs * 3))) {
+ if (unlikely(tg3_tx_avail(tp) <= (skb_shinfo(skb)->gso_segs * 3))) {
netif_stop_queue(tp->dev);
return NETDEV_TX_BUSY;
}
@@ -3958,7 +3968,7 @@ static int tg3_start_xmit_dma_bug(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(TX_BUFFS_AVAIL(tp) <= (skb_shinfo(skb)->nr_frags + 1))) {
+ if (unlikely(tg3_tx_avail(tp) <= (skb_shinfo(skb)->nr_frags + 1))) {
if (!netif_queue_stopped(dev)) {
netif_stop_queue(dev);
@@ -4108,12 +4118,10 @@ static int tg3_start_xmit_dma_bug(struct sk_buff *skb, struct net_device *dev)
tw32_tx_mbox((MAILBOX_SNDHOST_PROD_IDX_0 + TG3_64BIT_REG_LOW), entry);
tp->tx_prod = entry;
- if (unlikely(TX_BUFFS_AVAIL(tp) <= (MAX_SKB_FRAGS + 1))) {
- spin_lock(&tp->tx_lock);
+ if (unlikely(tg3_tx_avail(tp) <= (MAX_SKB_FRAGS + 1))) {
netif_stop_queue(dev);
- if (TX_BUFFS_AVAIL(tp) > TG3_TX_WAKEUP_THRESH)
+ if (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH)
netif_wake_queue(tp->dev);
- spin_unlock(&tp->tx_lock);
}
out_unlock:
@@ -11472,7 +11480,6 @@ static int __devinit tg3_init_one(struct pci_dev *pdev,
tp->grc_mode |= GRC_MODE_BSWAP_NONFRM_DATA;
#endif
spin_lock_init(&tp->lock);
- spin_lock_init(&tp->tx_lock);
spin_lock_init(&tp->indirect_lock);
INIT_WORK(&tp->reset_task, tg3_reset_task, tp);
diff --git a/drivers/net/tg3.h b/drivers/net/tg3.h
index ba2c98711c8..3ecf356cfb0 100644
--- a/drivers/net/tg3.h
+++ b/drivers/net/tg3.h
@@ -2079,9 +2079,9 @@ struct tg3 {
* lock: Held during reset, PHY access, timer, and when
* updating tg3_flags and tg3_flags2.
*
- * tx_lock: Held during tg3_start_xmit and tg3_tx only
- * when calling netif_[start|stop]_queue.
- * tg3_start_xmit is protected by netif_tx_lock.
+ * netif_tx_lock: Held during tg3_start_xmit. tg3_tx holds
+ * netif_tx_lock when it needs to call
+ * netif_wake_queue.
*
* Both of these locks are to be held with BH safety.
*
@@ -2118,8 +2118,6 @@ struct tg3 {
u32 tx_cons;
u32 tx_pending;
- spinlock_t tx_lock;
-
struct tg3_tx_buffer_desc *tx_ring;
struct tx_ring_info *tx_buffers;
dma_addr_t tx_desc_mapping;