+ huegtlbfs-fix-races-and-page-leaks-during-migration.patch added to -mm tree

* + huegtlbfs-fix-races-and-page-leaks-during-migration.patch added to -mm tree
@ 2019-02-12 22:22 akpm
  0 siblings, 0 replies; 2+ messages in thread
From: akpm @ 2019-02-12 22:22 UTC (permalink / raw)
  To: mm-commits, stable, n-horiguchi, mhocko, mgorman,
	kirill.shutemov, dave, aarcange, mike.kravetz


The patch titled
     Subject: hugetlbfs: fix races and page leaks during migration
has been added to the -mm tree.  Its filename is
     huegtlbfs-fix-races-and-page-leaks-during-migration.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/huegtlbfs-fix-races-and-page-leaks-during-migration.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/huegtlbfs-fix-races-and-page-leaks-during-migration.patch

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Mike Kravetz <mike.kravetz@oracle.com>
Subject: hugetlbfs: fix races and page leaks during migration

hugetlb pages should only be migrated if they are 'active'.  The routines
set/clear_page_huge_active() modify the active state of hugetlb pages. 
When a new hugetlb page is allocated at fault time, set_page_huge_active
is called before the page is locked.  Therefore, another thread could race
and migrate the page while it is being added to page table by the fault
code.  This race is somewhat hard to trigger, but can be seen by
strategically adding udelay to simulate worst case scheduling behavior. 
Depending on 'how' the code races, various BUG()s could be triggered.

To address this issue, simply delay the set_page_huge_active call until
after the page is successfully added to the page table.

Hugetlb pages can also be leaked at migration time if the pages are
associated with a file in an explicitly mounted hugetlbfs filesystem.  For
example, a test program which hole punches, faults and migrates pages in
such a file (1G in size) will eventually fail because it can not allocate
a page.  Reported counts and usage at time of failure:

node0
537     free_hugepages
1024    nr_hugepages
0       surplus_hugepages
node1
1000    free_hugepages
1024    nr_hugepages
0       surplus_hugepages

Filesystem                         Size  Used Avail Use% Mounted on
nodev                              4.0G  4.0G     0 100% /var/opt/hugepool

Note that the filesystem shows 4G of pages used, while actual usage is 511
pages (just under 1G).  Failed trying to allocate page 512.

If a hugetlb page is associated with an explicitly mounted filesystem,
this information in contained in the page_private field.  At migration
time, this information is not preserved.  To fix, simply transfer
page_private from old to new page at migration time if necessary.

Link: http://lkml.kernel.org/r/20190212221400.3512-1-mike.kravetz@oracle.com
Fixes: bcc54222309c ("mm: hugetlb: introduce page_huge_active")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/hugetlbfs/inode.c |   12 ++++++++++++
 mm/hugetlb.c         |    9 ++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

--- a/fs/hugetlbfs/inode.c~huegtlbfs-fix-races-and-page-leaks-during-migration
+++ a/fs/hugetlbfs/inode.c
@@ -859,6 +859,18 @@ static int hugetlbfs_migrate_page(struct
 	rc = migrate_huge_page_move_mapping(mapping, newpage, page);
 	if (rc != MIGRATEPAGE_SUCCESS)
 		return rc;
+
+	/*
+	 * page_private is subpool pointer in hugetlb pages.  Transfer to
+	 * new page.  PagePrivate is not associated with page_private for
+	 * hugetlb pages and can not be set here as only page_huge_active
+	 * pages can be migrated.
+	 */
+	if (page_private(page)) {
+		set_page_private(newpage, page_private(page));
+		set_page_private(page, 0);
+	}
+
 	if (mode != MIGRATE_SYNC_NO_COPY)
 		migrate_page_copy(newpage, page);
 	else
--- a/mm/hugetlb.c~huegtlbfs-fix-races-and-page-leaks-during-migration
+++ a/mm/hugetlb.c
@@ -3624,7 +3624,6 @@ retry_avoidcopy:
 	copy_user_huge_page(new_page, old_page, address, vma,
 			    pages_per_huge_page(h));
 	__SetPageUptodate(new_page);
-	set_page_huge_active(new_page);
 
 	mmu_notifier_range_init(&range, mm, haddr, haddr + huge_page_size(h));
 	mmu_notifier_invalidate_range_start(&range);
@@ -3645,6 +3644,7 @@ retry_avoidcopy:
 				make_huge_pte(vma, new_page, 1));
 		page_remove_rmap(old_page, true);
 		hugepage_add_new_anon_rmap(new_page, vma, haddr);
+		set_page_huge_active(new_page);
 		/* Make the old page be freed below */
 		new_page = old_page;
 	}
@@ -3790,7 +3790,6 @@ retry:
 		}
 		clear_huge_page(page, address, pages_per_huge_page(h));
 		__SetPageUptodate(page);
-		set_page_huge_active(page);
 
 		if (vma->vm_flags & VM_MAYSHARE) {
 			int err = huge_add_to_page_cache(page, mapping, idx);
@@ -3861,6 +3860,10 @@ retry:
 	}
 
 	spin_unlock(ptl);
+
+	/* May already be set if not newly allocated page */
+	set_page_huge_active(page);
+
 	unlock_page(page);
 out:
 	return ret;
@@ -4095,7 +4098,6 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 	 * the set_pte_at() write.
 	 */
 	__SetPageUptodate(page);
-	set_page_huge_active(page);
 
 	mapping = dst_vma->vm_file->f_mapping;
 	idx = vma_hugecache_offset(h, dst_vma, dst_addr);
@@ -4163,6 +4165,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 
 	spin_unlock(ptl);
+	set_page_huge_active(page);
 	if (vm_shared)
 		unlock_page(page);
 	ret = 0;
_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

huegtlbfs-fix-races-and-page-leaks-during-migration.patch


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