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    SubjectRe: [RFC] [PATCH 2.6.37-rc5-tip 5/20] 5: Uprobes: register/unregister probes.
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    On Thu, 2010-12-16 at 15:28 +0530, Srikar Dronamraju wrote:
    > +/* Returns 0 if it can install one probe */
    > +int register_uprobe(struct inode *inode, unsigned long offset,
    > + struct uprobe_consumer *consumer)
    > +{
    > + struct prio_tree_iter iter;
    > + struct list_head tmp_list;
    > + struct address_space *mapping;
    > + struct mm_struct *mm, *tmpmm;
    > + struct vm_area_struct *vma;
    > + struct uprobe *uprobe;
    > + int ret = -1;
    > +
    > + if (!inode || !consumer || consumer->next)
    > + return -EINVAL;
    > + uprobe = uprobes_add(inode, offset);
    > + INIT_LIST_HEAD(&tmp_list);
    > +
    > + mapping = inode->i_mapping;
    > +
    > + mutex_lock(&uprobes_mutex);
    > + if (uprobe->consumers) {
    > + ret = 0;
    > + goto consumers_add;
    > + }
    > +
    > + spin_lock(&mapping->i_mmap_lock);
    > + vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, 0, 0) {
    > + if (!atomic_inc_not_zero(&vma->vm_mm->mm_users))
    > + continue;
    > +
    > + mm = vma->vm_mm;
    > + if (!valid_vma(vma)) {
    > + mmput(mm);
    > + continue;
    > + }
    > +
    > + list_add(&mm->uprobes_list, &tmp_list);
    > + mm->uprobes_vaddr = vma->vm_start + offset;
    > + }
    > + spin_unlock(&mapping->i_mmap_lock);

    Both this and unregister are racy, what is to say:
    - the vma didn't get removed from the mm
    - no new matching vma got added

    > + if (list_empty(&tmp_list)) {
    > + ret = 0;
    > + goto consumers_add;
    > + }
    > + list_for_each_entry_safe(mm, tmpmm, &tmp_list, uprobes_list) {
    > + if (!install_uprobe(mm, uprobe))
    > + ret = 0;
    > + list_del(&mm->uprobes_list);
    > + mmput(mm);
    > + }
    > +
    > +consumers_add:
    > + add_consumer(uprobe, consumer);
    > + mutex_unlock(&uprobes_mutex);
    > + put_uprobe(uprobe);
    > + return ret;
    > +}
    > +


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