Re: [PATCH 0/3] hugetlbfs: use i_mmap_rwsem for better synchronization

[Andrew Morton]

On Mon,  3 Dec 2018 12:08:47 -0800 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:

> These patches are a follow up to the RFC,
> http://lkml.kernel.org/r/20181024045053.1467-1-mike.kravetz@xxxxxxxxxx
> Comments made by Naoya were addressed.
> 
> There are two primary issues addressed here:
> 1) For shared pmds, huge PE pointers returned by huge_pte_alloc can become
>    invalid via a call to huge_pmd_unshare by another thread.
> 2) hugetlbfs page faults can race with truncation causing invalid global
>    reserve counts and state.
> Both issues are addressed by expanding the use of i_mmap_rwsem.
> 
> These issues have existed for a long time.  They can be recreated with a
> test program that causes page fault/truncation races.  For simple mappings,
> this results in a negative HugePages_Rsvd count.  If racing with mappings
> that contain shared pmds, we can hit "BUG at fs/hugetlbfs/inode.c:444!" or
> Oops! as the result of an invalid memory reference.
> 
> I broke up the larger RFC into separate patches addressing each issue.
> Hopefully, this is easier to understand/review.

Three patches tagged for -stable and no reviewers yet.  Could people
please take a close look?