Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore)

Srikar Dronamraju
2018-08-13T10:03:42Z

> +
> +static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
> +{
> + struct delayed_uprobe *du;
> +
> + if (delayed_uprobe_check(uprobe, mm))
> + return 0;
> +
> + du = kzalloc(sizeof(*du), GFP_KERNEL);
> + if (!du)
> + return -ENOMEM;
> +
> + du->uprobe = uprobe;
> + du->mm = mm;
> + list_add(&du->list, &delayed_uprobe_list);
> + return 0;
> +}
> +

Should we keep the delayed uprobe list per mm?
That way we could avoid the global mutex lock.
And the list to traverse would also be small.

>
> @@ -378,8 +557,15 @@ static struct uprobe *get_uprobe(struct uprobe *uprobe)
>
> static void put_uprobe(struct uprobe *uprobe)
> {
> - if (atomic_dec_and_test(&uprobe->ref))
> + if (atomic_dec_and_test(&uprobe->ref)) {
> + /*
> + * If application munmap(exec_vma) before uprobe_unregister()
> + * gets called, we don't get a chance to remove uprobe from
> + * delayed_uprobe_list in remove_breakpoint(). Do it here.
> + */
> + delayed_uprobe_remove(uprobe, NULL);

I am not getting this part. If unmap happens before unregister,
why cant we use uprobe_munmap? what am I missing.

> kfree(uprobe);
> + }
> }
>