* [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
@ 2021-05-28 0:46 Mina Almasry
2021-05-28 18:43 ` Mike Kravetz
2021-06-01 0:37 ` Andrew Morton
0 siblings, 2 replies; 5+ messages in thread
From: Mina Almasry @ 2021-05-28 0:46 UTC (permalink / raw)
Cc: Mina Almasry, Axel Rasmussen, Peter Xu, linux-mm, Mike Kravetz,
Andrew Morton, linux-kernel, stable
The userfaultfd hugetlb tests detect 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 if there exists 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.
Signed-off-by: Mina Almasry <almasrymina@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: linux-mm@kvack.org
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
---
mm/hugetlb.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ead5d12e0604..76e2a6efc165 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4925,10 +4925,20 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
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,
--
2.32.0.rc0.204.g9fa02ecfa5-goog
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
2021-05-28 0:46 [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY Mina Almasry
@ 2021-05-28 18:43 ` Mike Kravetz
2021-06-01 0:37 ` Andrew Morton
1 sibling, 0 replies; 5+ messages in thread
From: Mike Kravetz @ 2021-05-28 18:43 UTC (permalink / raw)
To: Mina Almasry
Cc: Axel Rasmussen, Peter Xu, linux-mm, Andrew Morton, linux-kernel, stable
On 5/27/21 5:46 PM, Mina Almasry wrote:
> The userfaultfd hugetlb tests detect a resv_huge_pages underflow. This
Perhaps say,
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 if there exists a page in the cache which already
To fix this, we first check if there is a page in the cache which already
> To fix this, we first if there exists 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.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Cc: Axel Rasmussen <axelrasmussen@google.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: linux-mm@kvack.org
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
>
> ---
> mm/hugetlb.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
Code changes are fine. Thanks,
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
--
Mike Kravetz
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
2021-05-28 0:46 [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY Mina Almasry
2021-05-28 18:43 ` Mike Kravetz
@ 2021-06-01 0:37 ` Andrew Morton
2021-06-01 2:49 ` Mina Almasry
1 sibling, 1 reply; 5+ messages in thread
From: Andrew Morton @ 2021-06-01 0:37 UTC (permalink / raw)
To: Mina Almasry
Cc: Axel Rasmussen, Peter Xu, linux-mm, Mike Kravetz, linux-kernel, stable
On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry <almasrymina@google.com> wrote:
> The userfaultfd hugetlb tests detect 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 if there exists 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.
>
> Signed-off-by: Mina Almasry <almasrymina@google.com>
> Cc: Axel Rasmussen <axelrasmussen@google.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: linux-mm@kvack.org
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-mm@kvack.org
> Cc: linux-kernel@vger.kernel.org
> Cc: stable@vger.kernel.org
Do we have a Fixes: for this, or is it an always-been-there issue?
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
2021-06-01 0:37 ` Andrew Morton
@ 2021-06-01 2:49 ` Mina Almasry
2021-06-01 16:59 ` Mike Kravetz
0 siblings, 1 reply; 5+ messages in thread
From: Mina Almasry @ 2021-06-01 2:49 UTC (permalink / raw)
To: Andrew Morton
Cc: Axel Rasmussen, Peter Xu, Linux-MM, Mike Kravetz, open list, stable
On Mon, May 31, 2021 at 5:37 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry <almasrymina@google.com> wrote:
>
> > The userfaultfd hugetlb tests detect 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 if there exists 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.
> >
> > Signed-off-by: Mina Almasry <almasrymina@google.com>
> > Cc: Axel Rasmussen <axelrasmussen@google.com>
> > Cc: Peter Xu <peterx@redhat.com>
> > Cc: linux-mm@kvack.org
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: linux-mm@kvack.org
> > Cc: linux-kernel@vger.kernel.org
> > Cc: stable@vger.kernel.org
>
> Do we have a Fixes: for this, or is it an always-been-there issue?
This reproduces as far back as 4.15 kernel. Looks like always-been-there issue.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY
2021-06-01 2:49 ` Mina Almasry
@ 2021-06-01 16:59 ` Mike Kravetz
0 siblings, 0 replies; 5+ messages in thread
From: Mike Kravetz @ 2021-06-01 16:59 UTC (permalink / raw)
To: Mina Almasry, Andrew Morton
Cc: Axel Rasmussen, Peter Xu, Linux-MM, open list, stable
On 5/31/21 7:49 PM, Mina Almasry wrote:
> On Mon, May 31, 2021 at 5:37 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>> On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry <almasrymina@google.com> wrote:
>>
>>
>> Do we have a Fixes: for this, or is it an always-been-there issue?
>
> This reproduces as far back as 4.15 kernel. Looks like always-been-there issue.
>
Specifically,
Fixes: 8fb5debc5fcd ("userfaultfd: hugetlbfs: add hugetlb_mcopy_atomic_pte for userfaultfd support")
--
Mike Kravetz
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-05-28 0:46 [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY Mina Almasry
2021-05-28 18:43 ` Mike Kravetz
2021-06-01 0:37 ` Andrew Morton
2021-06-01 2:49 ` Mina Almasry
2021-06-01 16:59 ` Mike Kravetz
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