Re: [PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.

Oleg Nesterov
2011-06-13T17:02:24Z

On 06/07, Srikar Dronamraju wrote:
>
> +static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
> + unsigned long vaddr, uprobe_opcode_t opcode)
> +{
> + struct page *old_page, *new_page;
> + void *vaddr_old, *vaddr_new;
> + struct vm_area_struct *vma;
> + unsigned long addr;
> + int ret;
> +
> + /* Read the page with vaddr into memory */
> + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 1, 1, &old_page, &vma);

Sorry if this was already discussed... But why we are using FOLL_WRITE here?
We are not going to write into this page, and this provokes the unnecessary
cow, no?

Also. This is called under down_read(mmap_sem), can't we race with
access_process_vm() modifying the same memory?

Oleg.