[PATCH 01/94] mm: Add vma_lookup()

Michel Lespinasse michel at lespinasse.org
Sat May 1 06:04:41 BST 2021

On Wed, Apr 28, 2021 at 03:35:43PM +0000, Liam Howlett wrote:
> Many places in the kernel use find_vma() to get a vma and then check the
> start address of the vma to ensure the next vma was not returned.
> Other places use the find_vma_intersection() call with add, addr + 1 as
> the range; looking for just the vma at a specific address.
> The third use of find_vma() is by developers who do not know that the
> function starts searching at the provided address upwards for the next
> vma.  This results in a bug that is often overlooked for a long time.
> Adding the new vma_lookup() function will allow for cleaner code by
> removing the find_vma() calls which check limits, making
> find_vma_intersection() calls of a single address to be shorter, and
> potentially reduce the incorrect uses of find_vma().
> Signed-off-by: Liam R. Howlett <Liam.Howlett at Oracle.com>

This seems like a good API to have, and I agree it's less error prone than
having every caller check the vma->vm_start address.

Minor nitpick, I would prefer if the implementation used find_vma()
and then checked the vma->vm_start address - I don't like using [i, i+1)
intervals to implement stabbing queries.

But other than that, I think this (and the other patches adding
corresponding call sites) is safe for merging.

Michel "walken" Lespinasse

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