Re: [PATCH v2 2.6.38-rc8-tip 4/20] 4: uprobes: Adding and remove a uprobe in a rb tree.

Thomas Gleixner
2011-03-15T13:40:16Z

On Mon, 14 Mar 2011, Srikar Dronamraju wrote:
>
> +static int valid_vma(struct vm_area_struct *vma)

bool perpaps ?

> +{
> + if (!vma->vm_file)
> + return 0;
> +
> + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) ==
> + (VM_READ|VM_EXEC))

Looks more correct than the code it replaces :)

> + return 1;
> +
> + return 0;
> +}
> +

> +static struct rb_root uprobes_tree = RB_ROOT;
> +static DEFINE_MUTEX(uprobes_mutex);
> +static DEFINE_SPINLOCK(treelock);

Why do you need a mutex and a spinlock ? Also the mutex is not
referenced.

> +static int match_inode(struct uprobe *uprobe, struct inode *inode,
> + struct rb_node **p)
> +{
> + struct rb_node *n = *p;
> +
> + if (inode < uprobe->inode)
> + *p = n->rb_left;
> + else if (inode > uprobe->inode)
> + *p = n->rb_right;
> + else
> + return 1;
> + return 0;
> +}
> +
> +static int match_offset(struct uprobe *uprobe, loff_t offset,
> + struct rb_node **p)
> +{
> + struct rb_node *n = *p;
> +
> + if (offset < uprobe->offset)
> + *p = n->rb_left;
> + else if (offset > uprobe->offset)
> + *p = n->rb_right;
> + else
> + return 1;
> + return 0;
> +}
> +
> +
> +/* Called with treelock held */
> +static struct uprobe *__find_uprobe(struct inode * inode,
> + loff_t offset, struct rb_node **near_match)
> +{
> + struct rb_node *n = uprobes_tree.rb_node;
> + struct uprobe *uprobe, *u = NULL;
> +
> + while (n) {
> + uprobe = rb_entry(n, struct uprobe, rb_node);
> + if (match_inode(uprobe, inode, &n)) {
> + if (near_match)
> + *near_match = n;
> + if (match_offset(uprobe, offset, &n)) {
> + atomic_inc(&uprobe->ref);
> + u = uprobe;
> + break;
> + }
> + }
> + }
> + return u;
> +}
> +
> +/*
> + * Find a uprobe corresponding to a given inode:offset
> + * Acquires treelock
> + */
> +static struct uprobe *find_uprobe(struct inode * inode, loff_t offset)
> +{
> + struct uprobe *uprobe;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&treelock, flags);
> + uprobe = __find_uprobe(inode, offset, NULL);
> + spin_unlock_irqrestore(&treelock, flags);

What's the calling context ? Do we really need a spinlock here for
walking the rb tree ?

> +
> +/* Should be called lock-less */

-ENOPARSE

> +static void put_uprobe(struct uprobe *uprobe)
> +{
> + if (atomic_dec_and_test(&uprobe->ref))
> + kfree(uprobe);
> +}
> +
> +static struct uprobe *uprobes_add(struct inode *inode, loff_t offset)
> +{
> + struct uprobe *uprobe, *cur_uprobe;
> +
> + __iget(inode);
> + uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
> +
> + if (!uprobe) {
> + iput(inode);
> + return NULL;
> + }

Please move the __iget() after the kzalloc()

> + uprobe->inode = inode;
> + uprobe->offset = offset;
> +
> + /* add to uprobes_tree, sorted on inode:offset */
> + cur_uprobe = insert_uprobe(uprobe);
> +
> + /* a uprobe exists for this inode:offset combination*/
> + if (cur_uprobe) {
> + kfree(uprobe);
> + uprobe = cur_uprobe;
> + iput(inode);
> + } else
> + init_rwsem(&uprobe->consumer_rwsem);

Please init stuff _before_ inserting not afterwards.

> +
> + return uprobe;
> +}
> +
> +/* Acquires uprobe->consumer_rwsem */
> +static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
> +{
> + struct uprobe_consumer *consumer;
> +
> + down_read(&uprobe->consumer_rwsem);
> + consumer = uprobe->consumers;
> + while (consumer) {
> + if (!consumer->filter || consumer->filter(consumer, current))
> + consumer->handler(consumer, regs);
> +
> + consumer = consumer->next;
> + }
> + up_read(&uprobe->consumer_rwsem);
> +}
> +
> +/* Acquires uprobe->consumer_rwsem */
> +static void add_consumer(struct uprobe *uprobe,
> + struct uprobe_consumer *consumer)
> +{
> + down_write(&uprobe->consumer_rwsem);
> + consumer->next = uprobe->consumers;
> + uprobe->consumers = consumer;
> + up_write(&uprobe->consumer_rwsem);
> + return;

pointless return

> +}
> +
> +/* Acquires uprobe->consumer_rwsem */

I'd prefer a comment about the return code over this redundant
information.

> +static int del_consumer(struct uprobe *uprobe,
> + struct uprobe_consumer *consumer)
> +{