zio-buf-kmalloc: fail on alloc, don't fail on store

This is a fix for a design bug for this buffer. Actually, the
vmalloc buffer already is like this (and cannot be different).
This allows simplifying chardev.c and fix some corner cases that
are currently misbehaving.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Federico Vaga <federico.vaga@gmail.com>

buffers/zio-buf-kmalloc.c

@@ -71,6 +71,13 @@ static struct zio_block *zbk_alloc_block(struct zio_bi *bi,
 
 	pr_debug("%s:%d\n", __func__, __LINE__);
 
+	/* alloc fails if we overflow the buffer size */
+	spin_lock(&bi->lock);
+	if (zbki->nitem >= bi->zattr_set.std_zattr[ZIO_ATTR_ZBUF_MAXLEN].value)
+		goto out_unlock;
+	zbki->nitem++;
+	spin_unlock(&bi->lock);
+
 	/* alloc item and data. Control remains null at this point */
 	item = kmem_cache_alloc(zbk_slab, gfp);
 	data = kmalloc(datalen, gfp);
@@ -88,6 +95,10 @@ out_free:
 	kfree(data);
 	kmem_cache_free(zbk_slab, item);
 	zio_free_control(ctrl);
+	spin_lock(&bi->lock);
+	zbki->nitem--;
+out_unlock:
+	spin_unlock(&bi->lock);
 	return NULL;
 }
 
@@ -96,14 +107,25 @@ static void zbk_free_block(struct zio_bi *bi, struct zio_block *block)
 {
 	struct zbk_item *item;
 	struct zbk_instance *zbki;
+	int awake = 0;
 
 	pr_debug("%s:%d\n", __func__, __LINE__);
 
 	item = to_item(block);
 	zbki = item->instance;
+
+	spin_lock(&bi->lock);
+	if ( ((bi->flags & ZIO_DIR) == ZIO_DIR_OUTPUT) &&
+	     zbki->nitem < bi->zattr_set.std_zattr[ZIO_ATTR_ZBUF_MAXLEN].value)
+		awake = 1;
+	zbki->nitem--;
+	spin_unlock(&bi->lock);
+
 	kfree(block->data);
 	zio_free_control(zio_get_ctrl(block));
 	kmem_cache_free(zbk_slab, item);
+	if (awake)
+		wake_up_interruptible(&bi->q);
 }
 
 /* When write() stores the first block, we try pushing it */
@@ -134,25 +156,17 @@ static int zbk_store_block(struct zio_bi *bi, struct zio_block *block)
 {
 	struct zbk_instance *zbki = to_zbki(bi);
 	struct zio_channel *chan = bi->chan;
-	struct zbk_item *item;
-	int awake = 0, pushed = 0, output;
+	struct zbk_item *item = to_item(block);
+	int awake = 0, pushed = 0, isempty;
+	int output = (bi->flags & ZIO_DIR) == ZIO_DIR_OUTPUT;
 
 	pr_debug("%s:%d (%p, %p)\n", __func__, __LINE__, bi, block);
 
-	if (unlikely(!zio_get_ctrl(block))) {
-		WARN_ON(1);
-		return -EINVAL;
-	}
-
-	item = to_item(block);
-	output = (bi->flags & ZIO_DIR) == ZIO_DIR_OUTPUT;
-
 	/* add to the buffer instance or push to the trigger */
 	spin_lock(&bi->lock);
-	if (zbki->nitem >= bi->zattr_set.std_zattr[ZIO_ATTR_ZBUF_MAXLEN].value)
-		goto out_unlock;
+	isempty = list_empty(&zbki->list);
 	list_add_tail(&item->list, &zbki->list);
-	if (!zbki->nitem) {
+	if (isempty) {
 		if (unlikely(output))
 			pushed = __try_push(bi, chan, block);
 		else
@@ -160,17 +174,12 @@ static int zbk_store_block(struct zio_bi *bi, struct zio_block *block)
 	}
 	if (pushed)
 		list_del(&item->list);
-	zbki->nitem += !pushed;
 	spin_unlock(&bi->lock);
 
 	/* if first input, awake user space */
 	if (awake)
 		wake_up_interruptible(&bi->q);
 	return 0;
-
-out_unlock:
-	spin_unlock(&bi->lock);
-	return -ENOSPC;
 }
 
 /* Retr is called by f->read (for input) or by the trigger (for output) */
@@ -180,23 +189,17 @@ static struct zio_block *zbk_retr_block(struct zio_bi *bi)
 	struct zbk_instance *zbki;
 	struct zio_ti *ti;
 	struct list_head *first;
-	int awake = 0;
 
 	zbki = to_zbki(bi);
 
 	spin_lock(&bi->lock);
-	if (!zbki->nitem || bi->flags & ZIO_BI_PUSHING)
+	if (list_empty(&zbki->list) || bi->flags & ZIO_BI_PUSHING)
 		goto out_unlock;
 	first = zbki->list.next;
 	item = list_entry(first, struct zbk_item, list);
 	list_del(&item->list);
-	if (zbki->nitem == bi->zattr_set.std_zattr[ZIO_ATTR_ZBUF_MAXLEN].value)
-		awake = 1;
-	zbki->nitem--;
 	spin_unlock(&bi->lock);
 
-	if (awake && ((bi->flags & ZIO_DIR) == ZIO_DIR_OUTPUT))
-		wake_up_interruptible(&bi->q);
 	pr_debug("%s:%d (%p, %p)\n", __func__, __LINE__, bi, item);
 	return &item->block;