From: Mike Kravetz <mike.kravetz@oracle.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>, Hugh Dickins <hughd@google.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Prakash Sangappa <prakash.sangappa@oracle.com>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: [PATCH RFC v2 0/1] hugetlbfs: Use i_mmap_rwsem for pmd share and fault/trunc
Date: Tue, 23 Oct 2018 21:50:52 -0700 [thread overview]
Message-ID: <20181024045053.1467-1-mike.kravetz@oracle.com> (raw)
This patch addresses issues with page fault/truncation synchronization.
The first issue was noticed as a negative hugetlb reserved page counts
during DB development testing. Code inspection revealed that the most
likely cause were races with truncate and page faults. In fact, I could
write a not too complicated program to cause the races and recreate the
issue.
A more dangerous issue exists when you introduce huge pmd sharing to
page fault/truncate races. The fist thing that happens in huge page
fault processing is a call to huge_pte_alloc to get a ptep. Suppose
that ptep points to a shared pmd. Now, another thread could perform
a truncate and unmap everyone mapping the file. huge_pmd_unshare can
be called for the mapping on which the first thread is operating.
huge_pmd_unshare can clear pud pointing to the pmd. After this, the
ptep points to another task's page table or worse. This leads to bad
things such as incorrect page map/reference counts or invaid memory
references.
Fix this all by modifying the usage of i_mmap_rwsem to cover
fault/truncate races as well as handling of shared pmds
Mike Kravetz (1):
hugetlbfs: use i_mmap_rwsem for pmd sharing and truncate/fault sync
fs/hugetlbfs/inode.c | 21 ++++++++++----
mm/hugetlb.c | 65 +++++++++++++++++++++++++++++++++-----------
mm/rmap.c | 10 +++++++
mm/userfaultfd.c | 11 ++++++--
4 files changed, 84 insertions(+), 23 deletions(-)
--
2.17.2
next reply other threads:[~2018-10-24 4:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-24 4:50 Mike Kravetz [this message]
2018-10-24 4:50 ` [PATCH RFC v2 1/1] hugetlbfs: use i_mmap_rwsem for pmd sharing and truncate/fault sync Mike Kravetz
2018-10-26 0:42 ` Naoya Horiguchi
2018-10-30 21:54 ` Mike Kravetz
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