Re: [PATCH] mm: mempolicy: fix the wrong return value and potential pages leak of mbind

[Yang Shi]

On 10/30/19 9:31 PM, Andrew Morton wrote:
> On Wed, 30 Oct 2019 11:14:58 -0700 Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> wrote:
>
> > On 10/30/19 9:58 AM, Yang Shi wrote:
> > > The commit d883544515aa ("mm: mempolicy: make the behavior consistent
> > > when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified") fixed the return
> > > value of mbind() for a couple of corner cases.  But, it altered the
> > > errno for some other cases, for example, mbind() should return -EFAULT
> > > when part or all of the memory range specified by nodemask and maxnode
> > > points  outside your accessible address space, or there was an unmapped
> > > hole in the specified memory range specified by addr and len.
> > >
> > > Fixed this by preserving the errno returned by queue_pages_range().
> > > And, the pagelist may be not empty even though queue_pages_range()
> > > returns error, put the pages back to LRU since mbind_range() is not called
> > > to really apply the policy so those pages should not be migrated, this
> > > is also the old behavior before the problematic commit.
> > Forgot fixes tag.
> >
> > Fixes: d883544515aa ("mm: mempolicy: make the behavior consistent when
> > MPOL_MF_MOVE* and MPOL_MF_STRICT were specified")
> What's the relationship between this patch and
> http://lkml.kernel.org/r/201910291756045288126@xxxxxxxxx?

They are irrelevant. The commit d883544515aa ("mm: mempolicy: make the 
behavior consistent
when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified") override the 
-EFAULT return value of queue_pages_range() by -EIO mistakenly and 
missed putting non-empty pagelist back, this patch is aimed to fix the 
two issues.

I think Li Xinhai found the return value override problem during 
debugging his patch.