| Date | Fri, 7 Oct 2011 20:37:40 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v5 3.1.0-rc4-tip 18/26] uprobes: slot allocation. |
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On 09/20, Srikar Dronamraju wrote: > > - * valid_vma: Verify if the specified vma is an executable vma > + * valid_vma: Verify if the specified vma is an executable vma, > + * but not an XOL vma. > * - Return 1 if the specified virtual address is in an > - * executable vma. > + * executable vma, but not in an XOL vma. > */ > static bool valid_vma(struct vm_area_struct *vma) > { > + struct uprobes_xol_area *area = vma->vm_mm->uprobes_xol_area; > + > if (!vma->vm_file) > return false; > > + if (area && (area->vaddr == vma->vm_start)) > + return false;
Could you explain why do we need this "but not an XOL vma" check? xol_vma->vm_file is always NULL, no?
> +static struct uprobes_xol_area *xol_alloc_area(void) > +{ > + struct uprobes_xol_area *area = NULL; > + > + area = kzalloc(sizeof(*area), GFP_KERNEL); > + if (unlikely(!area)) > + return NULL; > + > + area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long), > + GFP_KERNEL); > + > + if (!area->bitmap) > + goto fail; > + > + init_waitqueue_head(&area->wq); > + spin_lock_init(&area->slot_lock); > + if (!xol_add_vma(area) && !current->mm->uprobes_xol_area) { > + task_lock(current); > + if (!current->mm->uprobes_xol_area) { > + current->mm->uprobes_xol_area = area; > + task_unlock(current); > + return area; > + } > + task_unlock(current);
But you can't rely on task_lock(), you can race with another thread with the same ->mm. I guess you need mmap_sem or xchg().
> static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, > unsigned long vaddr) > { > - /* TODO: Yet to be implemented */ > + if (xol_get_insn_slot(uprobe, vaddr) && !pre_xol(uprobe, regs)) { > + set_instruction_pointer(regs, current->utask->xol_vaddr);
set_instruction_pointer() looks unneded, pre_xol() has already changed regs->ip.
Oleg.
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