Re: [PATCH] mm: fix potential pte_unmap_unlock pte error

[Shijie Luo]

On 2020/10/16 22:05, osalvador@xxxxxxx wrote:
> On 2020-10-16 15:42, Michal Hocko wrote:
> > OK, I finally managed to convince my friday brain to think and grasped
> > what the code is intended to do. The loop is hairy and we want to
> > prevent from spurious EIO when all the pages are on a proper node. So
> > the check has to be done inside the loop. Anyway I would find the
> > following fix less error prone and easier to follow
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index eddbe4e56c73..8cc1fc9c4d13 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -525,7 +525,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
> > unsigned long addr,
> >      unsigned long flags = qp->flags;
> >      int ret;
> >      bool has_unmovable = false;
> > -    pte_t *pte;
> > +    pte_t *pte, *mapped_pte;
> >      spinlock_t *ptl;
> >
> >      ptl = pmd_trans_huge_lock(pmd, vma);
> > @@ -539,7 +539,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
> > unsigned long addr,
> >      if (pmd_trans_unstable(pmd))
> >          return 0;
> >
> > -    pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> > +    mapped_pte = pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);
> >      for (; addr != end; pte++, addr += PAGE_SIZE) {
> >          if (!pte_present(*pte))
> >              continue;
> > @@ -571,7 +571,7 @@ static int queue_pages_pte_range(pmd_t *pmd,
> > unsigned long addr,
> >          } else
> >              break;
> >      }
> > -    pte_unmap_unlock(pte - 1, ptl);
> > +    pte_unmap_unlock(mapped_pte, ptl);
> >      cond_resched();
> >
> >      if (has_unmovable)
>
> It is more clear to grasp, definitely.
Yeah, this one is more comprehensible, I 'll send a v2 patch, thank you.