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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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