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It's not possible for this scenario to happen in practice, so this check just adds confusion. There are two callers - the one from vma_expand() which unconditionally sets expand true, and the one from vma_merge_existing_range() (note that vma_merge_new_range() ultimately invokes vma_expand()). The vma_merge_existing_range() case will nearly always set expand, should a merge be indicated. In the one instance where it will not, adjust will always be set to a non-NULL value. Unfortunately this is super unclear, which is a big hint that refactoring is required - and it's something I've already started working on - so I will take this as a signal to increase the priority on this. So this has to be a no unfortunately, but thank you very much highlighting this as it clearly indicates the need to improve this, which is hugely valuable! Thanks, Lorenzo On Thu, Jan 16, 2025 at 10:50:05AM +0800, Liu Ye wrote: > Add VM_WARN_ON to prevent 'adjust' from accessing NULL pointers > when 'adjust' is NULL and 'expanded' is false or 'adj_start' is > not zero. > Signed-off-by: Liu Ye > --- > mm/vma.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/vma.c b/mm/vma.c > index 31c9c6f51c9f..36b5ac675504 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -641,6 +641,7 @@ static int commit_merge(struct vma_merge_struct *vmg, > > init_multi_vma_prep(&vp, vmg->vma, adjust, remove, remove2); > > + VM_WARN_ON(!adjust && (!expanded || adj_start)); > VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma && > vp.anon_vma != adjust->anon_vma); > > -- > 2.25.1 >