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authorHugh Dickins <hughd@google.com>2018-11-30 14:10:47 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-12-05 19:42:38 +0100
commitdc62803e271decb287929d44789fe9170eec5ba7 (patch)
tree4dff193c0dc6aadafa13d07f081c337fc9df92da /mm
parent8dcbb5f21567c3a85a7e4ec781d0e49ea174397d (diff)
mm/khugepaged: collapse_shmem() do not crash on Compound
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@google.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Jerome Glisse <jglisse@redhat.com> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Cc: Matthew Wilcox <willy@infradead.org> Cc: <stable@vger.kernel.org> [4.8+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/khugepaged.c10
1 files changed, 9 insertions, 1 deletions
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;