linux-kernel - [PATCH v2 1/2] huegtlbfs: on restore reserve error path retain subpool reservation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20190328234704.27083-2-mike.kravetz@oracle.com>
Date:   Thu, 28 Mar 2019 16:47:03 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Davidlohr Bueso <dave@...olabs.net>
Cc:     Joonsoo Kim <iamjoonsoo.kim@....com>,
        Michal Hocko <mhocko@...nel.org>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH v2 1/2] huegtlbfs: on restore reserve error path retain subpool reservation

When a huge page is allocated, PagePrivate() is set if the allocation
consumed a reservation.  When freeing a huge page, PagePrivate is checked.
If set, it indicates the reservation should be restored.  PagePrivate
being set at free huge page time mostly happens on error paths.

When huge page reservations are created, a check is made to determine if
the mapping is associated with an explicitly mounted filesystem.  If so,
pages are also reserved within the filesystem.  The default action when
freeing a huge page is to decrement the usage count in any associated
explicitly mounted filesystem.  However, if the reservation is to be
restored the reservation/use count within the filesystem should not be
decrementd.  Otherwise, a subsequent page allocation and free for the same
mapping location will cause the file filesystem usage to go 'negative'.

Filesystem                         Size  Used Avail Use% Mounted on
nodev                              4.0G -4.0M  4.1G    - /opt/hugepool

To fix, when freeing a huge page do not adjust filesystem usage if
PagePrivate() is set to indicate the reservation should be restored.

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 mm/hugetlb.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f79ae4e42159..8651d6a602f9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1268,12 +1268,23 @@ void free_huge_page(struct page *page)
 	ClearPagePrivate(page);

 	/*
-	 * A return code of zero implies that the subpool will be under its
-	 * minimum size if the reservation is not restored after page is free.
-	 * Therefore, force restore_reserve operation.
+	 * If PagePrivate() was set on page, page allocation consumed a
+	 * reservation.  If the page was associated with a subpool, there
+	 * would have been a page reserved in the subpool before allocation
+	 * via hugepage_subpool_get_pages().  Since we are 'restoring' the
+	 * reservtion, do not call hugepage_subpool_put_pages() as this will
+	 * remove the reserved page from the subpool.
 	 */
-	if (hugepage_subpool_put_pages(spool, 1) == 0)
-		restore_reserve = true;
+	if (!restore_reserve) {
+		/*
+		 * A return code of zero implies that the subpool will be
+		 * under its minimum size if the reservation is not restored
+		 * after page is free.  Therefore, force restore_reserve
+		 * operation.
+		 */
+		if (hugepage_subpool_put_pages(spool, 1) == 0)
+			restore_reserve = true;
+	}

 	spin_lock(&hugetlb_lock);
 	clear_page_huge_active(page);
-- 
2.20.1