Re: [PATCH] Initialise mmu_notifier_range correctly

Jerome Glisse
2019-01-03T15:05:26Z

On Thu, Jan 03, 2019 at 06:43:13AM -0800, Matthew Wilcox wrote:
> On Thu, Jan 03, 2019 at 09:31:16AM -0500, Jerome Glisse wrote:
> > On Wed, Jan 02, 2019 at 04:21:26PM -0800, Matthew Wilcox wrote:
> > >
> > > One of the paths in follow_pte_pmd() initialised the mmu_notifier_range
> > > incorrectly.
> > >
> > > Signed-off-by: Matthew Wilcox <willy@infradead.org>
> > > Fixes: ac46d4f3c432 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
> > > Tested-by: Dave Chinner <dchinner@redhat.com>
> >
> > Actually now that i have read the code again this is not ok to
> > do so. The caller of follow_pte_pmd() will call range_init and
> > follow pmd will only update the range address. So existing code
> > is ok.
>
> I think you need to re-read your own patch.
>
> `git show ac46d4f3c43241ffa23d5bf36153a0830c0e02cc`
>
> @@ -4058,10 +4059,10 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsigned long address,
> if (!pmdpp)
> goto out;
>
> - if (start && end) {
> - *start = address & PMD_MASK;
> - *end = *start + PMD_SIZE;
> - mmu_notifier_invalidate_range_start(mm, *start, *end);
> + if (range) {
> + mmu_notifier_range_init(range, mm, address & PMD_MASK,
> + (address & PMD_MASK) + PMD_SIZE);
> + mmu_notifier_invalidate_range_start(range);
>
> ... so it's fine to call range_init() *here*.
>
> @@ -4069,17 +4070,17 @@ static int __follow_pte_pmd(struct mm_struct *mm, unsign
> ed long address,
> [...]
> if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
> goto out;
>
> - if (start && end) {
> - *start = address & PAGE_MASK;
> - *end = *start + PAGE_SIZE;
> - mmu_notifier_invalidate_range_start(mm, *start, *end);
> + if (range) {
> + range->start = address & PAGE_MASK;
> + range->end = range->start + PAGE_SIZE;
> + mmu_notifier_invalidate_range_start(range);
>
> ... but then *not* here later in the same function? You're not making
> any sense.

Ok i see that the patch that add the reason why mmu notifier is
call have been drop. So yes using range_init in follow_pte_pmd
is fine. With that other patch the reasons is set by the caller
of follow_pte_pmd and using range_init would have overwritten
it.

So this patch is fine for current tree. Sorry i was thinking with
the other patch included in mind.

Cheers,
Jérôme