[PATCH v1 6/9] mm: Change dup_mmap() recovery

[Pedro Falcato]

On Tue, Sep 09, 2025 at 03:09:42PM -0400, Liam R. Howlett wrote:
> When the dup_mmap() fails during the vma duplication or setup, don't
> write the XA_ZERO entry in the vma tree.  Instead, destroy the tree and
> free the new resources, leaving an empty vma tree.
> 
> Using XA_ZERO introduced races where the vma could be found between
> dup_mmap() dropping all locks and exit_mmap() taking the locks.  The
> race can occur because the mm can be reached through the other trees
> via successfully copied vmas and other methods such as the swapoff code.
> 
> XA_ZERO was marking the location to stop vma removal and pagetable
> freeing.  The newly created arguments to the unmap_vmas() and
> free_pgtables() serve this function.
> 
> Replacing the XA_ZERO entry use with the new argument list also means
> the checks for xa_is_zero() are no longer necessary so these are also
> removed.
> 
> Signed-off-by: Liam R. Howlett <Liam.Howlett at oracle.com>

Reviewed-by: Pedro Falcato <pfalcato at suse.de>

-- 
Pedro