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

Srikar Dronamraju
2011-03-15T17:36:53Z

* Thomas Gleixner <tglx@linutronix.de> [2011-03-15 14:38:33]:

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

Okay,

>
> > +{
> > + 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 :)

Yes, Steven Rostedt has already pointed this out.

>
> > + 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.

We can move the mutex to the next patch, (i.e register/unregister
patch), where it gets used. mutex for now serializes
register_uprobe/unregister_uprobe/mmap_uprobe.
This mutex is the one that guards mm->uprobes_list.

>
> > +/*
> > + * 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 ?
>

find_uprobe() gets called from unregister_uprobe and on probe hit from
uprobe_notify_resume. I am not sure if its a good idea to walk the tree
as and when the tree is changing either because of a insertion or
deletion of a probe.

> > +
> > +/* 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()

Okay.

>
> > + 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.

Okay.

>
> > +
> > + 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

Okay,

>
> > +}
> > +
> > +/* Acquires uprobe->consumer_rwsem */
>
> I'd prefer a comment about the return code over this redundant
> information.
>

Okay,

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