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-crash-on-compound.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-khugepaged-collapse_shmem-do-not-crash-on-compound.patch
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------------------------------------------------------
From: Hugh Dickins <hughd@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- 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@xxxxxxxxxx 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
