The patch titled Subject: mm/khugepaged: collapse_shmem() do not crash on Compound has been added to the -mm tree. Its filename is mm-khugepaged-collapse_shmem-do-not-crash-on-compound.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-khugepaged-collapse_shmem-do-not... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-collapse_shmem-do-not...

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------------------------------------------------------ From: Hugh Dickins hughd@google.com Subject: 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 ---

--- a/mm/khugepaged.c~mm-khugepaged-collapse_shmem-do-not-crash-on-compound +++ a/mm/khugepaged.c @@ -1399,7 +1399,15 @@ static void collapse_shmem(struct mm_str */ 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; _

Patches currently in -mm which might be from hughd@google.com are

mm-huge_memory-rename-freeze_page-to-unmap_page.patch mm-huge_memory-splitting-set-mappingindex-before-unfreeze.patch mm-huge_memory-fix-lockdep-complaint-on-32-bit-i_size_read.patch mm-khugepaged-collapse_shmem-stop-if-punched-or-truncated.patch mm-khugepaged-fix-crashes-due-to-misaccounted-holes.patch mm-khugepaged-collapse_shmem-remember-to-clear-holes.patch mm-khugepaged-minor-reorderings-in-collapse_shmem.patch mm-khugepaged-collapse_shmem-without-freezing-new_page.patch mm-khugepaged-collapse_shmem-do-not-crash-on-compound.patch mm-khugepaged-fix-the-xas_create_range-error-path.patch mm-put_and_wait_on_page_locked-while-page-is-migrated.patch