mm/dmapool.c: take lock only once in dma_pool_free()

dma_pool_free() scans for the page to free in the pool list holding the
pool lock.  Then it releases the lock basically to acquire it immediately
again.  Modify the code to only take the lock once.

This will do some additional loops and computations with the lock held in
if memory debugging is activated.  If it is not activated the only new
operations with this lock is one if and one substraction.
Signed-off-by: NRolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/dmapool.c

@@ -355,20 +355,15 @@ EXPORT_SYMBOL(dma_pool_alloc);
 
 static struct dma_page *pool_find_page(struct dma_pool *pool, dma_addr_t dma)
 {
-	unsigned long flags;
 	struct dma_page *page;
 
-	spin_lock_irqsave(&pool->lock, flags);
 	list_for_each_entry(page, &pool->page_list, page_list) {
 		if (dma < page->dma)
 			continue;
 		if (dma < (page->dma + pool->allocation))
-			goto done;
+			return page;
 	}
-	page = NULL;
- done:
-	spin_unlock_irqrestore(&pool->lock, flags);
-	return page;
+	return NULL;
 }
 
 /**
@@ -386,8 +381,10 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	unsigned long flags;
 	unsigned int offset;
 
+	spin_lock_irqsave(&pool->lock, flags);
 	page = pool_find_page(pool, dma);
 	if (!page) {
+		spin_unlock_irqrestore(&pool->lock, flags);
 		if (pool->dev)
 			dev_err(pool->dev,
 				"dma_pool_free %s, %p/%lx (bad dma)\n",
@@ -401,6 +398,7 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	offset = vaddr - page->vaddr;
 #ifdef	DMAPOOL_DEBUG
 	if ((dma - page->dma) != offset) {
+		spin_unlock_irqrestore(&pool->lock, flags);
 		if (pool->dev)
 			dev_err(pool->dev,
 				"dma_pool_free %s, %p (bad vaddr)/%Lx\n",
@@ -418,6 +416,7 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 				chain = *(int *)(page->vaddr + chain);
 				continue;
 			}
+			spin_unlock_irqrestore(&pool->lock, flags);
 			if (pool->dev)
 				dev_err(pool->dev, "dma_pool_free %s, dma %Lx "
 					"already free\n", pool->name,
@@ -432,7 +431,6 @@ void dma_pool_free(struct dma_pool *pool, void *vaddr, dma_addr_t dma)
 	memset(vaddr, POOL_POISON_FREED, pool->size);
 #endif
 
-	spin_lock_irqsave(&pool->lock, flags);
 	page->in_use--;
 	*(int *)vaddr = page->offset;
 	page->offset = offset;