Re: [PATCH v2 2.6.38-rc8-tip 3/20] 3: uprobes: Breakground page replacement.

Stephen Wilson
2011-03-14T16:58:53Z

On Mon, Mar 14, 2011 at 07:04:33PM +0530, Srikar Dronamraju wrote:
> +/**
> + * read_opcode - read the opcode at a given virtual address.
> + * @tsk: the probed task.
> + * @vaddr: the virtual address to store the opcode.
> + * @opcode: location to store the read opcode.
> + *
> + * For task @tsk, read the opcode at @vaddr and store it in @opcode.
> + * Return 0 (success) or a negative errno.
> + */
> +int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
> + uprobe_opcode_t *opcode)
> +{
> + struct vm_area_struct *vma;
> + struct page *page;
> + void *vaddr_new;
> + int ret;
> +
> + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma);
> + if (ret <= 0)
> + return -EFAULT;
> + ret = -EFAULT;
> +
> + /*
> + * check if the page we are interested is read-only mapped
> + * Since we are interested in text pages, Our pages of interest
> + * should be mapped read-only.
> + */
> + if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) ==
> + (VM_READ|VM_EXEC))
> + goto put_out;
> +
> + lock_page(page);
> + vaddr_new = kmap_atomic(page, KM_USER0);
> + vaddr &= ~PAGE_MASK;
> + memcpy(&opcode, vaddr_new + vaddr, uprobe_opcode_sz);
> + kunmap_atomic(vaddr_new, KM_USER0);
> + unlock_page(page);
> + ret = uprobe_opcode_sz;

This looks wrong. We should be setting ret = 0 on success here?

> +
> +put_out:
> + put_page(page); /* we did a get_page in the beginning */
> + return ret;
> +}

--
steve