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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 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) {

So what happens if xol_add_vma() succeeds, but we find
->uprobes_xol_area set?

> + task_lock(current);
> + if (!current->mm->uprobes_xol_area) {

Having to re-test it under this lock seems to suggest it could.

> + current->mm->uprobes_xol_area = area;
> + task_unlock(current);
> + return area;

This function would be so much easier to read if the success case (this
here I presume) would not be nested 2 deep.

> + }
> + task_unlock(current);
> + }

at which point you could end up with two extra vmas? Because there's no
freeing of the result of xol_add_vma().

> +fail:
> + kfree(area->bitmap);
> + kfree(area);
> + return current->mm->uprobes_xol_area;
> +}


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