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


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