Re: mmap-rb-7 [was Re: /proc/<n>/maps growing...]

[Manfred Spraul]

> +/*
> + * vma->vm_start/vm_end cannot change under us because the caller is
required
> + * to hold the mmap_sem in write mode. We need to get the spinlock
only
> + * before relocating the vma range ourself.
> + */

There is one exception to that rule: a growable stack grows with
mmap_sem only acquired in read mode. vm_start can change on platforms
where the stack grows down, probably vm_end changes on platforms where
the stack grows upwards.

> - lock_vma_mappings(vma);
> - spin_lock(&vma->vm_mm->page_table_lock);
>  vma->vm_pgoff += (end - vma->vm_start) >> PAGE_SHIFT;
> + lock_vma_mappings(vma);
> + spin_lock(&mm->page_table_lock);
> vma->vm_start = end;

Could be wrong with concurrent stack faults.

--
    Manfred