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Message-Id: <20181204103715.144118790@linuxfoundation.org>
Date: Tue, 4 Dec 2018 11:50:07 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Jerome Glisse <jglisse@...hat.com>,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
Matthew Wilcox <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 12/50] mm/khugepaged: collapse_shmem() do not crash on Compound
4.9-stable review patch. If anyone has any objections, please let me know.
------------------
commit 06a5e1268a5fb9c2b346a3da6b97e85f2eba0f07 upstream.
collapse_shmem()'s VM_BUG_ON_PAGE(PageTransCompound) was unsafe: before
it holds page lock of the first page, racing truncation then extension
might conceivably have inserted a hugepage there already. Fail with the
SCAN_PAGE_COMPOUND result, instead of crashing (CONFIG_DEBUG_VM=y) or
otherwise mishandling the unexpected hugepage - though later we might
code up a more constructive way of handling it, with SCAN_SUCCESS.
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1811261529310.2275@eggly.anvils
Fixes: f3f0e1d2150b2 ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Jerome Glisse <jglisse@...hat.com>
Cc: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: <stable@...r.kernel.org> [4.8+]
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
mm/khugepaged.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b87bd43993bd..e0cfc3a54b6a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1400,7 +1400,15 @@ static void collapse_shmem(struct mm_struct *mm,
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageUptodate(page), page);
- VM_BUG_ON_PAGE(PageTransCompound(page), page);
+
+ /*
+ * If file was truncated then extended, or hole-punched, before
+ * we locked the first page, then a THP might be there already.
+ */
+ if (PageTransCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ goto out_unlock;
+ }
if (page_mapping(page) != mapping) {
result = SCAN_TRUNCATED;
--
2.17.1
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