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>

diff --git a/drivers/net/mv643xx_eth.c b/drivers/net/mv643xx_eth.c
index c41ae42..b3bf864 100644 (file)
--- 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