diff options
| author | Hugh Dickins <hughd@google.com> | 2018-11-30 14:10:47 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2018-11-30 14:56:15 -0800 |
| commit | 06a5e1268a5fb9c2b346a3da6b97e85f2eba0f07 (patch) | |
| tree | a2ccdfe76f11e07f2538884cb9c607cc90079492 | |
| parent | 87c460a0bded56195b5eb497d44709777ef7b415 (diff) | |
mm/khugepaged: collapse_shmem() do not crash on Compound
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>
| -rw-r--r-- | mm/khugepaged.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 55930cbed3fd..2c5fe4f7a0c6 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1399,7 +1399,15 @@ 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; |