96 lines
3.3 KiB
Diff
96 lines
3.3 KiB
Diff
Bugzilla: 1093084
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Upstream-status: 3.15 and stable CC'd
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From 85cc8301cbedcf3049ce15de6f3c2b9e935d0d76 Mon Sep 17 00:00:00 2001
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From: Vlastimil Babka <vbabka@suse.cz>
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Date: Mon, 7 Apr 2014 15:37:50 -0700
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Subject: [PATCH] mm: try_to_unmap_cluster() should lock_page() before mlocking
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A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin
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fuzzing with trinity. The call site try_to_unmap_cluster() does not lock
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the pages other than its check_page parameter (which is already locked).
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The BUG_ON in mlock_vma_page() is not documented and its purpose is
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somewhat unclear, but apparently it serializes against page migration,
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which could otherwise fail to transfer the PG_mlocked flag. This would
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not be fatal, as the page would be eventually encountered again, but
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NR_MLOCK accounting would become distorted nevertheless. This patch adds
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a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that
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effect.
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The call site try_to_unmap_cluster() is fixed so that for page !=
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check_page, trylock_page() is attempted (to avoid possible deadlocks as we
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already have check_page locked) and mlock_vma_page() is performed only
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upon success. If the page lock cannot be obtained, the page is left
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without PG_mlocked, which is again not a problem in the whole unevictable
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memory design.
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Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
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Signed-off-by: Bob Liu <bob.liu@oracle.com>
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Reported-by: Sasha Levin <sasha.levin@oracle.com>
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Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
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Cc: Michel Lespinasse <walken@google.com>
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Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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Acked-by: Rik van Riel <riel@redhat.com>
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Cc: David Rientjes <rientjes@google.com>
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Cc: Mel Gorman <mgorman@suse.de>
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Cc: Hugh Dickins <hughd@google.com>
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Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
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Cc: <stable@vger.kernel.org>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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mm/mlock.c | 2 ++
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mm/rmap.c | 14 ++++++++++++--
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2 files changed, 14 insertions(+), 2 deletions(-)
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diff --git a/mm/mlock.c b/mm/mlock.c
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index 192e6eebe4f2..1b12dfad0794 100644
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--- a/mm/mlock.c
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+++ b/mm/mlock.c
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@@ -79,6 +79,7 @@ void clear_page_mlock(struct page *page)
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*/
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void mlock_vma_page(struct page *page)
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{
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+ /* Serialize with page migration */
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BUG_ON(!PageLocked(page));
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if (!TestSetPageMlocked(page)) {
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@@ -153,6 +154,7 @@ unsigned int munlock_vma_page(struct page *page)
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{
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unsigned int nr_pages;
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+ /* For try_to_munlock() and to serialize with page migration */
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BUG_ON(!PageLocked(page));
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if (TestClearPageMlocked(page)) {
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diff --git a/mm/rmap.c b/mm/rmap.c
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index 068522d8502a..b99c74271fec 100644
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--- a/mm/rmap.c
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+++ b/mm/rmap.c
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@@ -1389,9 +1389,19 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
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BUG_ON(!page || PageAnon(page));
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if (locked_vma) {
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- mlock_vma_page(page); /* no-op if already mlocked */
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- if (page == check_page)
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+ if (page == check_page) {
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+ /* we know we have check_page locked */
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+ mlock_vma_page(page);
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ret = SWAP_MLOCK;
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+ } else if (trylock_page(page)) {
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+ /*
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+ * If we can lock the page, perform mlock.
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+ * Otherwise leave the page alone, it will be
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+ * eventually encountered again later.
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+ */
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+ mlock_vma_page(page);
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+ unlock_page(page);
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+ }
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continue; /* don't unmap */
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}
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--
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1.9.0
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