[03/04 mm-patch, rfc] Add lightweight rwlock to net/dccp/ccid.c (was Re: [mm-patch] bluetooth: use GFP_ATOMIC in *_sock_create's sk_alloc)

[Frederik Deweerdt]

This patch is part of the lw_rwlock patchset, it removes the
ccids_{read,write}_{lock,unlock} functions which have been moved
to linux/lw_rwlock.h and made more generic.
                                          
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@xxxxxxxxx>

--- v2.6.18-rc2-mm1~ori/net/dccp/ccid.c	2006-06-18 03:49:35.000000000 +0200
+++ v2.6.18-rc2-mm1/net/dccp/ccid.c	2006-07-28 16:19:32.000000000 +0200
@@ -12,48 +12,11 @@
  */
 
 #include "ccid.h"
+#include <linux/lw_rwlock.h>
 
 static struct ccid_operations *ccids[CCID_MAX];
-#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
-static atomic_t ccids_lockct = ATOMIC_INIT(0);
-static DEFINE_SPINLOCK(ccids_lock);
-
-/*
- * The strategy is: modifications ccids vector are short, do not sleep and
- * veeery rare, but read access should be free of any exclusive locks.
- */
-static void ccids_write_lock(void)
-{
-	spin_lock(&ccids_lock);
-	while (atomic_read(&ccids_lockct) != 0) {
-		spin_unlock(&ccids_lock);
-		yield();
-		spin_lock(&ccids_lock);
-	}
-}
-
-static inline void ccids_write_unlock(void)
-{
-	spin_unlock(&ccids_lock);
-}
+static DEFINE_LW_RWLOCK(ccids_lock);
 
-static inline void ccids_read_lock(void)
-{
-	atomic_inc(&ccids_lockct);
-	spin_unlock_wait(&ccids_lock);
-}
-
-static inline void ccids_read_unlock(void)
-{
-	atomic_dec(&ccids_lockct);
-}
-
-#else
-#define ccids_write_lock() do { } while(0)
-#define ccids_write_unlock() do { } while(0)
-#define ccids_read_lock() do { } while(0)
-#define ccids_read_unlock() do { } while(0)
-#endif
 
 static kmem_cache_t *ccid_kmem_cache_create(int obj_size, const char *fmt,...)
 {
@@ -103,13 +66,13 @@ int ccid_register(struct ccid_operations
 	if (ccid_ops->ccid_hc_tx_slab == NULL)
 		goto out_free_rx_slab;
 
-	ccids_write_lock();
+	lw_write_lock(&ccids_lock);
 	err = -EEXIST;
 	if (ccids[ccid_ops->ccid_id] == NULL) {
 		ccids[ccid_ops->ccid_id] = ccid_ops;
 		err = 0;
 	}
-	ccids_write_unlock();
+	lw_write_unlock(&ccids_lock);
 	if (err != 0)
 		goto out_free_tx_slab;
 
@@ -131,9 +94,9 @@ EXPORT_SYMBOL_GPL(ccid_register);
 
 int ccid_unregister(struct ccid_operations *ccid_ops)
 {
-	ccids_write_lock();
+	lw_write_lock(&ccids_lock);
 	ccids[ccid_ops->ccid_id] = NULL;
-	ccids_write_unlock();
+	lw_write_unlock(&ccids_lock);
 
 	ccid_kmem_cache_destroy(ccid_ops->ccid_hc_tx_slab);
 	ccid_ops->ccid_hc_tx_slab = NULL;
@@ -152,15 +115,15 @@ struct ccid *ccid_new(unsigned char id, 
 	struct ccid_operations *ccid_ops;
 	struct ccid *ccid = NULL;
 
-	ccids_read_lock();
+	lw_read_lock(&ccids_lock);
 #ifdef CONFIG_KMOD
 	if (ccids[id] == NULL) {
 		/* We only try to load if in process context */
-		ccids_read_unlock();
+		lw_read_unlock(&ccids_lock);
 		if (gfp & GFP_ATOMIC)
 			goto out;
 		request_module("net-dccp-ccid-%d", id);
-		ccids_read_lock();
+		lw_read_lock(&ccids_lock);
 	}
 #endif
 	ccid_ops = ccids[id];
@@ -170,7 +133,7 @@ struct ccid *ccid_new(unsigned char id, 
 	if (!try_module_get(ccid_ops->ccid_owner))
 		goto out_unlock;
 
-	ccids_read_unlock();
+	lw_read_unlock(&ccids_lock);
 
 	ccid = kmem_cache_alloc(rx ? ccid_ops->ccid_hc_rx_slab :
 				     ccid_ops->ccid_hc_tx_slab, gfp);
@@ -191,7 +154,7 @@ struct ccid *ccid_new(unsigned char id, 
 out:
 	return ccid;
 out_unlock:
-	ccids_read_unlock();
+	lw_read_unlock(&ccids_lock);
 	goto out;
 out_free_ccid:
 	kmem_cache_free(rx ? ccid_ops->ccid_hc_rx_slab :
@@ -235,10 +198,10 @@ static void ccid_delete(struct ccid *cci
 			ccid_ops->ccid_hc_tx_exit(sk);
 		kmem_cache_free(ccid_ops->ccid_hc_tx_slab,  ccid);
 	}
-	ccids_read_lock();
+	lw_read_lock(&ccids_lock);
 	if (ccids[ccid_ops->ccid_id] != NULL)
 		module_put(ccid_ops->ccid_owner);
-	ccids_read_unlock();
+	lw_read_unlock(&ccids_lock);
 }
 
 void ccid_hc_rx_delete(struct ccid *ccid, struct sock *sk)