mv643xx_eth: Fix race condition in mv643xx_eth_free_tx_descs

mv643xx_eth: Fix race condition in mv643xx_eth_free_tx_descs

This bug was found and isolated by Thibaut VARENE <T-Bone@parisc-linux.org>
and Jarek Poplawski <jarkao2@o2.pl>.  This patch is a modification of their
fixes.  We acquire and release the lock for each descriptor that is freed
to minimize the time the lock is held.

Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/net/mv643xx_eth.c b/drivers/net/mv643xx_eth.c
index c41ae4286eea..b3bf86422734 100644
--- a/drivers/net/mv643xx_eth.c
+++ b/drivers/net/mv643xx_eth.c
@@ -314,6 +314,13 @@ int mv643xx_eth_free_tx_descs(struct net_device *dev, int force)
 
         while (mp->tx_desc_count > 0) {
                 spin_lock_irqsave(&mp->lock, flags);
+
+                /* tx_desc_count might have changed before acquiring the lock */
+                if (mp->tx_desc_count <= 0) {
+                        spin_unlock_irqrestore(&mp->lock, flags);
+                        return released;
+                }
+
                 tx_index = mp->tx_used_desc_q;
                 desc = &mp->p_tx_desc_area[tx_index];
                 cmd_sts = desc->cmd_sts;
@@ -332,13 +339,13 @@ int mv643xx_eth_free_tx_descs(struct net_device *dev, int force)
                 if (skb)
                         mp->tx_skb[tx_index] = NULL;
 
-                spin_unlock_irqrestore(&mp->lock, flags);
-
                 if (cmd_sts & ETH_ERROR_SUMMARY) {
                         printk("%s: Error in TX\n", dev->name);
                         mp->stats.tx_errors++;
                 }
 
+                spin_unlock_irqrestore(&mp->lock, flags);
+
                 if (cmd_sts & ETH_TX_FIRST_DESC)
                         dma_unmap_single(NULL, addr, count, DMA_TO_DEVICE);
                 else