Re: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation.

[Peter Zijlstra]

On Tue, 2011-09-20 at 17:33 +0530, Srikar Dronamraju wrote:
> +static unsigned long xol_take_insn_slot(struct uprobes_xol_area *area)
> +{
> +       unsigned long slot_addr, flags;
> +       int slot_nr;
> +
> +       do {
> +               spin_lock_irqsave(&area->slot_lock, flags);
> +               slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
> +               if (slot_nr < UINSNS_PER_PAGE) {
> +                       __set_bit(slot_nr, area->bitmap);
> +                       slot_addr = area->vaddr +
> +                                       (slot_nr * UPROBES_XOL_SLOT_BYTES);
> +                       atomic_inc(&area->slot_count);
> +               }
> +               spin_unlock_irqrestore(&area->slot_lock, flags);
> +               if (slot_nr >= UINSNS_PER_PAGE)
> +                       xol_wait_event(area);
> +
> +       } while (slot_nr >= UINSNS_PER_PAGE);
> +
> +       return slot_addr;
> +}

> +static void xol_free_insn_slot(struct task_struct *tsk)
> +{
> +       struct uprobes_xol_area *area;
> +       unsigned long vma_end;
> +       unsigned long slot_addr;
> +
> +       if (!tsk->mm || !tsk->mm->uprobes_xol_area || !tsk->utask)
> +               return;
> +
> +       slot_addr = tsk->utask->xol_vaddr;
> +
> +       if (unlikely(!slot_addr || IS_ERR_VALUE(slot_addr)))
> +               return;
> +
> +       area = tsk->mm->uprobes_xol_area;
> +       vma_end = area->vaddr + PAGE_SIZE;
> +       if (area->vaddr <= slot_addr && slot_addr < vma_end) {
> +               int slot_nr;
> +               unsigned long offset = slot_addr - area->vaddr;
> +               unsigned long flags;
> +
> +               slot_nr = offset / UPROBES_XOL_SLOT_BYTES;
> +               if (slot_nr >= UINSNS_PER_PAGE)
> +                       return;
> +
> +               spin_lock_irqsave(&area->slot_lock, flags);
> +               __clear_bit(slot_nr, area->bitmap);
> +               spin_unlock_irqrestore(&area->slot_lock, flags);
> +               atomic_dec(&area->slot_count);
> +               if (waitqueue_active(&area->wq))
> +                       wake_up(&area->wq);
> +               tsk->utask->xol_vaddr = 0;
> +       }
> +} 

So if you want to keep that slot_lock, you might as well make
->slot_count a normal integer.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/