[Xen-devel] [PATCH] netfront: Lockdep fixes

[Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>]

netfront contains two locking problems found by lockdep:

1. rx_lock is a normal spinlock, and tx_lock is an irq spinlock.  This
   means that in normal use, tx_lock may be taken by an interrupt routine
   while rx_lock is held.  However, netif_disconnect_backend takes them
   in the order tx_lock->rx_lock, which could lead to a deadlock.  Reverse
   them.
2. rx_lock can also be used in softirq context, so it should be taken/released
   with spin_(un)lock_bh.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: Chris Wright <chrisw@xxxxxxxxxxxx>
Cc: Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>

diff -r a69029562c74 linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c
--- a/linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c      Thu Apr 12 
14:13:33 2007 -0700
+++ b/linux-2.6-xen-sparse/drivers/xen/netfront/netfront.c      Thu Apr 12 
14:19:42 2007 -0700
@@ -622,14 +622,14 @@ static int network_open(struct net_devic
 
        memset(&np->stats, 0, sizeof(np->stats));
 
-       spin_lock(&np->rx_lock);
+       spin_lock_bh(&np->rx_lock);
        if (netfront_carrier_ok(np)) {
                network_alloc_rx_buffers(dev);
                np->rx.sring->rsp_event = np->rx.rsp_cons + 1;
                if (RING_HAS_UNCONSUMED_RESPONSES(&np->rx))
                        netif_rx_schedule(dev);
        }
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
 
        network_maybe_wake_tx(dev);
 
@@ -1307,10 +1307,10 @@ static int netif_poll(struct net_device 
        int pages_flipped = 0;
        int err;
 
-       spin_lock(&np->rx_lock);
+       spin_lock_bh(&np->rx_lock);
 
        if (unlikely(!netfront_carrier_ok(np))) {
-               spin_unlock(&np->rx_lock);
+               spin_unlock_bh(&np->rx_lock);
                return 0;
        }
 
@@ -1478,7 +1478,7 @@ err:
                local_irq_restore(flags);
        }
 
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
 
        return more_to_do;
 }
@@ -1520,7 +1520,7 @@ static void netif_release_rx_bufs(struct
 
        skb_queue_head_init(&free_list);
 
-       spin_lock(&np->rx_lock);
+       spin_lock_bh(&np->rx_lock);
 
        for (id = 0; id < NET_RX_RING_SIZE; id++) {
                if ((ref = np->grant_rx_ref[id]) == GRANT_INVALID_REF) {
@@ -1588,7 +1588,7 @@ static void netif_release_rx_bufs(struct
        while ((skb = __skb_dequeue(&free_list)) != NULL)
                dev_kfree_skb(skb);
 
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
 }
 
 static int network_close(struct net_device *dev)
@@ -1708,8 +1708,8 @@ static int network_connect(struct net_de
        IPRINTK("device %s has %sing receive path.\n",
                dev->name, np->copying_receiver ? "copy" : "flipp");
 
+       spin_lock_bh(&np->rx_lock);
        spin_lock_irq(&np->tx_lock);
-       spin_lock(&np->rx_lock);
 
        /*
         * Recovery procedure:
@@ -1761,7 +1761,7 @@ static int network_connect(struct net_de
        network_tx_buf_gc(dev);
        network_alloc_rx_buffers(dev);
 
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
        spin_unlock_irq(&np->tx_lock);
 
        return 0;
@@ -1818,7 +1818,7 @@ static ssize_t store_rxbuf_min(struct cl
        if (target > RX_MAX_TARGET)
                target = RX_MAX_TARGET;
 
-       spin_lock(&np->rx_lock);
+       spin_lock_bh(&np->rx_lock);
        if (target > np->rx_max_target)
                np->rx_max_target = target;
        np->rx_min_target = target;
@@ -1827,7 +1827,7 @@ static ssize_t store_rxbuf_min(struct cl
 
        network_alloc_rx_buffers(netdev);
 
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
        return len;
 }
 
@@ -1861,7 +1861,7 @@ static ssize_t store_rxbuf_max(struct cl
        if (target > RX_MAX_TARGET)
                target = RX_MAX_TARGET;
 
-       spin_lock(&np->rx_lock);
+       spin_lock_bh(&np->rx_lock);
        if (target < np->rx_min_target)
                np->rx_min_target = target;
        np->rx_max_target = target;
@@ -1870,7 +1870,7 @@ static ssize_t store_rxbuf_max(struct cl
 
        network_alloc_rx_buffers(netdev);
 
-       spin_unlock(&np->rx_lock);
+       spin_unlock_bh(&np->rx_lock);
        return len;
 }
 
@@ -2033,10 +2033,10 @@ static void netif_disconnect_backend(str
 static void netif_disconnect_backend(struct netfront_info *info)
 {
        /* Stop old i/f to prevent errors whilst we rebuild the state. */
+       spin_lock_bh(&info->rx_lock);
        spin_lock_irq(&info->tx_lock);
-       spin_lock(&info->rx_lock);
        netfront_carrier_off(info);
-       spin_unlock(&info->rx_lock);
+       spin_unlock_bh(&info->rx_lock);
        spin_unlock_irq(&info->tx_lock);
 
        if (info->irq)


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