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

[Oleg Nesterov]

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.

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