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SubjectRe: [PATCH v5 3.1.0-rc4-tip 4/26] uprobes: Define hooks for mmap/munmap.
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On Mon, 2011-09-26 at 21:14 +0530, Srikar Dronamraju wrote:
>
> > > +
> > > +/*
> > > + * Called from mmap_region.
> > > + * called with mm->mmap_sem acquired.
> > > + *
> > > + * Return -ve no if we fail to insert probes and we cannot
> > > + * bail-out.
> > > + * Return 0 otherwise. i.e :
> > > + * - successful insertion of probes
> > > + * - (or) no possible probes to be inserted.
> > > + * - (or) insertion of probes failed but we can bail-out.
> > > + */
> > > +int mmap_uprobe(struct vm_area_struct *vma)
> > > +{
> > > + struct list_head tmp_list;
> > > + struct uprobe *uprobe, *u;
> > > + struct inode *inode;
> > > + int ret = 0;
> > > +
> > > + if (!valid_vma(vma))
> > > + return ret; /* Bail-out */
> > > +
> > > + inode = igrab(vma->vm_file->f_mapping->host);
> > > + if (!inode)
> > > + return ret;
> > > +
> > > + INIT_LIST_HEAD(&tmp_list);
> > > + mutex_lock(&uprobes_mmap_mutex);
> > > + build_probe_list(inode, &tmp_list);
> > > + list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
> > > + loff_t vaddr;
> > > +
> > > + list_del(&uprobe->pending_list);
> > > + if (!ret && uprobe->consumers) {
> > > + vaddr = vma->vm_start + uprobe->offset;
> > > + vaddr -= vma->vm_pgoff << PAGE_SHIFT;
> > > + if (vaddr < vma->vm_start || vaddr >= vma->vm_end)
> > > + continue;
> > > + ret = install_breakpoint(vma->vm_mm, uprobe);
> > > +
> > > + if (ret && (ret == -ESRCH || ret == -EEXIST))
> > > + ret = 0;
> > > + }
> > > + put_uprobe(uprobe);
> > > + }
> > > +
> > > + mutex_unlock(&uprobes_mmap_mutex);
> > > + iput(inode);
> > > + return ret;
> > > +}
> > > +
> > > +static void dec_mm_uprobes_count(struct vm_area_struct *vma,
> > > + struct inode *inode)
> > > +{
> > > + struct uprobe *uprobe;
> > > + struct rb_node *n;
> > > + unsigned long flags;
> > > +
> > > + n = uprobes_tree.rb_node;
> > > + spin_lock_irqsave(&uprobes_treelock, flags);
> > > + uprobe = __find_uprobe(inode, 0, &n);
> > > +
> > > + /*
> > > + * If indeed there is a probe for the inode and with offset zero,
> > > + * then lets release its reference. (ref got thro __find_uprobe)
> > > + */
> > > + if (uprobe)
> > > + put_uprobe(uprobe);
> > > + for (; n; n = rb_next(n)) {
> > > + loff_t vaddr;
> > > +
> > > + uprobe = rb_entry(n, struct uprobe, rb_node);
> > > + if (uprobe->inode != inode)
> > > + break;
> > > + vaddr = vma->vm_start + uprobe->offset;
> > > + vaddr -= vma->vm_pgoff << PAGE_SHIFT;
> > > + if (vaddr < vma->vm_start || vaddr >= vma->vm_end)
> > > + continue;
> > > + atomic_dec(&vma->vm_mm->mm_uprobes_count);
> > > + }
> > > + spin_unlock_irqrestore(&uprobes_treelock, flags);
> > > +}
> > > +
> > > +/*
> > > + * Called in context of a munmap of a vma.
> > > + */
> > > +void munmap_uprobe(struct vm_area_struct *vma)
> > > +{
> > > + struct inode *inode;
> > > +
> > > + if (!valid_vma(vma))
> > > + return; /* Bail-out */
> > > +
> > > + if (!atomic_read(&vma->vm_mm->mm_uprobes_count))
> > > + return;
> > > +
> > > + inode = igrab(vma->vm_file->f_mapping->host);
> > > + if (!inode)
> > > + return;
> > > +
> > > + dec_mm_uprobes_count(vma, inode);
> > > + iput(inode);
> > > + return;
> > > +}
> >
> > One has to wonder why mmap_uprobe() can be one function but
> > munmap_uprobe() cannot.
> >
>
> I didnt understand this comment, Can you please elaborate?
> mmap_uprobe uses build_probe_list and munmap_uprobe uses
> dec_mm_uprobes_count.

Ah, I missed build_probe_list(), but I didn't see a reason for the
existence of dec_mm_uprobe_count(), the name doesn't make sense and the
content is 'small' enough to just put in munmap_uprobe.

To me it looks similar to the list iteration you have in mmap_uprobe(),
you didn't split that out into another function either.


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