* + mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch added to -mm tree
@ 2021-06-01 0:33 akpm
0 siblings, 0 replies; only message in thread
From: akpm @ 2021-06-01 0:33 UTC (permalink / raw)
To: almasrymina, axelrasmussen, mike.kravetz, mm-commits, peterx, stable
The patch titled
Subject: mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY
has been added to the -mm tree. Its filename is
mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch
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------------------------------------------------------
From: Mina Almasry <almasrymina@google.com>
Subject: mm, hugetlb: fix simple resv_huge_pages underflow on UFFDIO_COPY
The userfaultfd hugetlb tests cause a resv_huge_pages underflow. This
happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on an
index for which we already have a page in the cache. When this happens,
we allocate a second page, double consuming the reservation, and then fail
to insert the page into the cache and return -EEXIST.
To fix this, we first check if there is a page in the cache which already
consumed the reservation, and return -EEXIST immediately if so.
There is still a rare condition where we fail to copy the page contents
AND race with a call for hugetlb_no_page() for this index and again we
will underflow resv_huge_pages. That is fixed in a more complicated patch
not targeted for -stable.
Test:
Hacked the code locally such that resv_huge_pages underflows produce
a warning, then:
./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10
2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
./tools/testing/selftests/vm/userfaultfd hugetlb 10
2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success
Both tests succeed and produce no warnings. After the
test runs number of free/resv hugepages is correct.
[mike.kravetz@oracle.com: changelog fixes]
Link: https://lkml.kernel.org/r/20210528004649.85298-1-almasrymina@google.com
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/hugetlb.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- a/mm/hugetlb.c~mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy
+++ a/mm/hugetlb.c
@@ -4889,10 +4889,20 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
if (!page)
goto out;
} else if (!*pagep) {
- ret = -ENOMEM;
+ /* If a page already exists, then it's UFFDIO_COPY for
+ * a non-missing case. Return -EEXIST.
+ */
+ if (vm_shared &&
+ hugetlbfs_pagecache_present(h, dst_vma, dst_addr)) {
+ ret = -EEXIST;
+ goto out;
+ }
+
page = alloc_huge_page(dst_vma, dst_addr, 0);
- if (IS_ERR(page))
+ if (IS_ERR(page)) {
+ ret = -ENOMEM;
goto out;
+ }
ret = copy_huge_page_from_user(page,
(const void __user *) src_addr,
_
Patches currently in -mm which might be from almasrymina@google.com are
mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch
mm-hugetlb-fix-racy-resv_huge_pages-underflow-on-uffdio_copy.patch
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2021-06-01 0:33 + mm-hugetlb-fix-simple-resv_huge_pages-underflow-on-uffdio_copy.patch added to -mm tree akpm
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