[PATCH] shaper.c: fix locking

[Christoph Hellwig <hch@xxxxxx>]

 o use a semaphore instead of an opencoded and racy lock
 o move locking out of shaper_kick and into the callers - most just
   released the lock before calling shaper_kick
 o remove in_interrupt() tests.  from ->close we can always block, from
   ->hard_start_xmit and timer context never


Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Index: linux-2.6/include/linux/if_shaper.h
===================================================================
--- linux-2.6.orig/include/linux/if_shaper.h    2005-04-30 10:17:19.000000000 
+0200
+++ linux-2.6/include/linux/if_shaper.h 2005-05-27 13:47:47.000000000 +0200
@@ -23,7 +23,7 @@
        __u32 shapeclock;
        unsigned long recovery; /* Time we can next clock a packet out on
                                   an empty queue */
-        unsigned long locked;
+       struct semaphore sem;
         struct net_device_stats stats;
        struct net_device *dev;
        int  (*hard_start_xmit) (struct sk_buff *skb,
@@ -38,7 +38,6 @@
        int (*hard_header_cache)(struct neighbour *neigh, struct hh_cache *hh);
        void (*header_cache_update)(struct hh_cache *hh, struct net_device 
*dev, unsigned char *  haddr);
        struct net_device_stats* (*get_stats)(struct net_device *dev);
-       wait_queue_head_t  wait_queue;
        struct timer_list timer;
 };
 
Index: linux-2.6/drivers/net/shaper.c
===================================================================
--- linux-2.6.orig/drivers/net/shaper.c 2005-04-30 10:17:15.000000000 +0200
+++ linux-2.6/drivers/net/shaper.c      2005-05-27 13:50:41.000000000 +0200
@@ -100,35 +100,8 @@
 
 #define SHAPER_BANNER  "CymruNet Traffic Shaper BETA 0.04 for Linux 2.1\n"
 
-/*
- *     Locking
- */
- 
-static int shaper_lock(struct shaper *sh)
-{
-       /*
-        *      Lock in an interrupt must fail
-        */
-       while (test_and_set_bit(0, &sh->locked))
-       {
-               if (!in_interrupt())
-                       sleep_on(&sh->wait_queue);
-               else
-                       return 0;
-                       
-       }
-       return 1;
-}
-
 static void shaper_kick(struct shaper *sh);
 
-static void shaper_unlock(struct shaper *sh)
-{
-       clear_bit(0, &sh->locked);
-       wake_up(&sh->wait_queue);
-       shaper_kick(sh);
-}
-
 /*
  *     Compute clocks on a buffer
  */
@@ -157,17 +130,15 @@
  *     Throw a frame at a shaper.
  */
   
-static int shaper_qframe(struct shaper *shaper, struct sk_buff *skb)
+
+static int shaper_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
+       struct shaper *shaper = dev->priv;
        struct sk_buff *ptr;
    
-       /*
-        *      Get ready to work on this shaper. Lock may fail if its
-        *      an interrupt and locked.
-        */
-        
-       if(!shaper_lock(shaper))
-               return -1;
+       if (down_trylock(&shaper->sem))
+               return -1;
+
        ptr=shaper->sendq.prev;
        
        /*
@@ -260,7 +231,8 @@
                 dev_kfree_skb(ptr);
                 shaper->stats.collisions++;
        }
-       shaper_unlock(shaper);
+       shaper_kick(shaper);
+       up(&shaper->sem);
        return 0;
 }
 
@@ -297,8 +269,13 @@
  
 static void shaper_timer(unsigned long data)
 {
-       struct shaper *sh=(struct shaper *)data;
-       shaper_kick(sh);
+       struct shaper *shaper = (struct shaper *)data;
+
+       if (!down_trylock(&shaper->sem)) {
+               shaper_kick(shaper);
+               up(&shaper->sem);
+       } else
+               mod_timer(&shaper->timer, jiffies);
 }
 
 /*
@@ -311,19 +288,6 @@
        struct sk_buff *skb;
        
        /*
-        *      Shaper unlock will kick
-        */
-        
-       if (test_and_set_bit(0, &shaper->locked))
-       {
-               if(sh_debug)
-                       printk("Shaper locked.\n");
-               mod_timer(&shaper->timer, jiffies);
-               return;
-       }
-
-               
-       /*
         *      Walk the list (may be empty)
         */
         
@@ -364,8 +328,6 @@
         
        if(skb!=NULL)
                mod_timer(&shaper->timer, SHAPERCB(skb)->shapeclock);
-
-       clear_bit(0, &shaper->locked);
 }
 
 
@@ -376,14 +338,12 @@
 static void shaper_flush(struct shaper *shaper)
 {
        struct sk_buff *skb;
-       if(!shaper_lock(shaper))
-       {
-               printk(KERN_ERR "shaper: shaper_flush() called by an irq!\n");
-               return;
-       }
+
+       down(&shaper->sem);
        while((skb=skb_dequeue(&shaper->sendq))!=NULL)
                dev_kfree_skb(skb);
-       shaper_unlock(shaper);
+       shaper_kick(shaper);
+       up(&shaper->sem);
 }
 
 /*
@@ -426,13 +386,6 @@
  *     ARP and other resolutions and not before.
  */
 
-
-static int shaper_start_xmit(struct sk_buff *skb, struct net_device *dev)
-{
-       struct shaper *sh=dev->priv;
-       return shaper_qframe(sh, skb);
-}
-
 static struct net_device_stats *shaper_get_stats(struct net_device *dev)
 {
        struct shaper *sh=dev->priv;
@@ -623,7 +576,6 @@
        init_timer(&sh->timer);
        sh->timer.function=shaper_timer;
        sh->timer.data=(unsigned long)sh;
-       init_waitqueue_head(&sh->wait_queue);
 }
 
 /*