Re: [PATCH v3] ipc: Modify message queue accounting to not take kernel data structures into account

[Davidlohr Bueso <dave-h16yJtLeMjHk1uMJSBkQmQ@public.gmane.org>]

While on the subject, after taking another look at where and how we
calculate the treesize, I think we can remove this check when checking
attributes (mqueue_attr_ok -- which itself could use some simplifying):

	mq_treesize = attr->mq_maxmsg * sizeof(struct msg_msg) +
		min_t(unsigned int, attr->mq_maxmsg, MQ_PRIO_MAX) *
		sizeof(struct posix_msg_tree_node);

	total_size = attr->mq_maxmsg * attr->mq_msgsize;

	if (total_size + mq_treesize < total_size)
		return -EOVERFLOW;
		^^^ this condition is never true, so we never return EOVERFLOW.
	return 0;

The below gets rid of this bogus check and refactors similar code,
introducing a mqueue_sizeof() helper to do the job of calculating total
mqueue overhead.

Thoughts?

Thanks,
Davidlohr

diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 161a180..a5d0c9e 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -209,6 +209,31 @@ try_again:
 	return msg;
 }
 
+/*
+ * We used to allocate a static array of pointers and account
+ * the size of that array as well as one msg_msg struct per
+ * possible message into the queue size. That's no longer
+ * accurate as the queue is now an rbtree and will grow and
+ * shrink depending on usage patterns.  We can, however, still
+ * account one msg_msg struct per message, but the nodes are
+ * allocated depending on priority usage, and most programs
+ * only use one, or a handful, of priorities.  However, since
+ * this is pinned memory, we need to assume worst case, so
+ * that means the min(mq_maxmsg, max_priorities) * struct
+ * posix_msg_tree_node.
+ */
+static inline unsigned long mqueue_sizeof(struct mqueue_inode_info *info)
+{
+	unsigned long mq_treesize, mq_max_msgsize;
+
+	mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
+		min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
+		sizeof(struct posix_msg_tree_node);
+
+	mq_max_msgsize = info->attr.mq_maxmsg * info->attr.mq_msgsize;
+	return mq_treesize + mq_max_msgsize; /* bytes */
+}
+
 static struct inode *mqueue_get_inode(struct super_block *sb,
 		struct ipc_namespace *ipc_ns, umode_t mode,
 		struct mq_attr *attr)
@@ -229,7 +254,7 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 
 	if (S_ISREG(mode)) {
 		struct mqueue_inode_info *info;
-		unsigned long mq_bytes, mq_treesize;
+		unsigned long mq_bytes;
 
 		inode->i_fop = &mqueue_file_operations;
 		inode->i_size = FILENT_SIZE;
@@ -254,25 +279,8 @@ static struct inode *mqueue_get_inode(struct super_block *sb,
 			info->attr.mq_maxmsg = attr->mq_maxmsg;
 			info->attr.mq_msgsize = attr->mq_msgsize;
 		}
-		/*
-		 * We used to allocate a static array of pointers and account
-		 * the size of that array as well as one msg_msg struct per
-		 * possible message into the queue size. That's no longer
-		 * accurate as the queue is now an rbtree and will grow and
-		 * shrink depending on usage patterns.  We can, however, still
-		 * account one msg_msg struct per message, but the nodes are
-		 * allocated depending on priority usage, and most programs
-		 * only use one, or a handful, of priorities.  However, since
-		 * this is pinned memory, we need to assume worst case, so
-		 * that means the min(mq_maxmsg, max_priorities) * struct
-		 * posix_msg_tree_node.
-		 */
-		mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
-			min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
-			sizeof(struct posix_msg_tree_node);
 
-		mq_bytes = mq_treesize + (info->attr.mq_maxmsg *
-					  info->attr.mq_msgsize);
+		mq_bytes = mqueue_sizeof(info);
 
 		spin_lock(&mq_lock);
 		if (u->mq_bytes + mq_bytes < u->mq_bytes ||
@@ -371,7 +379,7 @@ static void mqueue_evict_inode(struct inode *inode)
 {
 	struct mqueue_inode_info *info;
 	struct user_struct *user;
-	unsigned long mq_bytes, mq_treesize;
+	unsigned long mq_bytes;
 	struct ipc_namespace *ipc_ns;
 	struct msg_msg *msg;
 
@@ -388,13 +396,7 @@ static void mqueue_evict_inode(struct inode *inode)
 	kfree(info->node_cache);
 	spin_unlock(&info->lock);
 
-	/* Total amount of bytes accounted for the mqueue */
-	mq_treesize = info->attr.mq_maxmsg * sizeof(struct msg_msg) +
-		min_t(unsigned int, info->attr.mq_maxmsg, MQ_PRIO_MAX) *
-		sizeof(struct posix_msg_tree_node);
-
-	mq_bytes = mq_treesize + (info->attr.mq_maxmsg *
-				  info->attr.mq_msgsize);
+	mq_bytes = mqueue_sizeof(info);
 
 	user = info->user;
 	if (user) {
@@ -692,9 +694,6 @@ static void remove_notification(struct mqueue_inode_info *info)
 
 static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
 {
-	int mq_treesize;
-	unsigned long total_size;
-
 	if (attr->mq_maxmsg <= 0 || attr->mq_msgsize <= 0)
 		return -EINVAL;
 	if (capable(CAP_SYS_RESOURCE)) {
@@ -709,12 +708,6 @@ static int mq_attr_ok(struct ipc_namespace *ipc_ns, struct mq_attr *attr)
 	/* check for overflow */
 	if (attr->mq_msgsize > ULONG_MAX/attr->mq_maxmsg)
 		return -EOVERFLOW;
-	mq_treesize = attr->mq_maxmsg * sizeof(struct msg_msg) +
-		min_t(unsigned int, attr->mq_maxmsg, MQ_PRIO_MAX) *
-		sizeof(struct posix_msg_tree_node);
-	total_size = attr->mq_maxmsg * attr->mq_msgsize;
-	if (total_size + mq_treesize < total_size)
-		return -EOVERFLOW;
 	return 0;
 }