On Tue, 4 Mar 2025 21:45:27 +0000 Yosry Ahmed <yosry.ahmed@xxxxxxxxx> wrote:
> On Mon, Mar 03, 2025 at 11:08:34AM +0000, Lorenzo Stoakes wrote:
> > Update move_vma() to use the threaded VRM object, de-duplicate code and
> > separate into smaller functions to aid readability and debug-ability.
> >
> > This in turn allows further simplification of expand_vma() as we can simply
> > thread VRM through the function.
> >
> > We also take the opportunity to abstract the account charging page count
> > into the VRM in order that we can correctly thread this through the
> > operation.
> >
> > We additionally do the same for tracking mm statistics - exec_vm, stack_vm,
> > data_vm, and locked_vm.
> >
> > As part of this change, we slightly modify when locked pages statistics are
> > counted for in mm_struct statistics. However this should cause no issues,
> > as there is no chance of underflow, nor will any rlimit failures occur as a
> > result.
> >
> > This is an intermediate step before a further refactoring of move_vma() in
> > order to aid review.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > ---
> [..]
> > +/*
> > + * Perform checks before attempting to write a VMA prior to it being
> > + * moved.
> > + */
> > +static unsigned long prep_move_vma(struct vma_remap_struct *vrm,
> > + unsigned long *vm_flags_ptr)
> > +{
> > + unsigned long err;
>
> I am getting a warning on mm-unstable because 'err' is sometimes used
> uninitialized, I think here:
>
> if (vma->vm_ops && vma->vm_ops->may_split) {
> if (vma->vm_start != old_addr)
> err = vma->vm_ops->may_split(vma, old_addr);
> if (!err && vma->vm_end != old_addr + old_len)
> err = vma->vm_ops->may_split(vma, old_addr + old_len);
> if (err)
> return err;
> }
yep, thanks. I added this:
--- a/mm/mremap.c~mm-mremap-initial-refactor-of-move_vma-fix
+++ a/mm/mremap.c
@@ -892,7 +892,7 @@ static void vrm_stat_account(struct vma_
static unsigned long prep_move_vma(struct vma_remap_struct *vrm,
unsigned long *vm_flags_ptr)
{
- unsigned long err;
+ unsigned long err = 0;
struct vm_area_struct *vma = vrm->vma;
unsigned long old_addr = vrm->addr;
unsigned long old_len = vrm->old_len;
_
