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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 /drivers/net/bnx2.h
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>
Diffstat (limited to 'drivers/net/bnx2.h')
-rw-r--r--drivers/net/bnx2.h12
1 files changed, 5 insertions, 7 deletions
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. */