Re: [RFC PATCH v4 4/6] uretprobes: return probe entry, prepare uretprobe

Oleg Nesterov
2013-03-04T16:50:00Z

On 03/04, Anton Arapov wrote:
>
> @@ -1085,6 +1093,7 @@ static int xol_add_vma(struct xol_area *area)
> {
> struct mm_struct *mm = current->mm;
> int ret = -EALREADY;
> + uprobe_opcode_t insn = UPROBE_SWBP_INSN;
>
> down_write(&mm->mmap_sem);
> if (mm->uprobes_state.xol_area)
> @@ -1106,6 +1115,13 @@ static int xol_add_vma(struct xol_area *area)
> smp_wmb(); /* pairs with get_xol_area() */
> mm->uprobes_state.xol_area = area;
> ret = 0;
> +
> + /*
> + * If we reached this place, we did allocate a new area. We want
> + * pre-alloc a slot for the return probes here.
> + */
> + xol_get_insn_slot(&insn);

Just change get_xol_area() to do set_bit(0, bitmap) and copy_to_page(page, int3)
(extacted from xol_get_insn_slot().

> @@ -1485,8 +1538,11 @@ static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
> *is_swbp = -EFAULT;
> }
>
> - if (!uprobe && test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags))
> + utask = get_utask();
> + if (!uprobe && hlist_empty(&utask->return_uprobes) &&
> + test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags)) {
> mmf_recalc_uprobes(mm);

Wait, I was wrong. We should not clear MMF_* if another thread has
->return_uprobes. Perhaps we should change uprobe_pre_sstep_notifier()
instead...

> down_read(&uprobe->register_rwsem);
> for (uc = uprobe->consumers; uc; uc = uc->next) {
> - int rc = uc->handler(uc, regs);
> + if (uc->handler)
> + rc = uc->handler(uc, regs);
> +
> + if (uc->rp_handler)
> + prepare_uretprobe(uprobe, regs); /* put bp at return */

Again, this is not right. We should do this only once after the main
loop.

Oleg.