The patch titled
Subject: mm/khugepaged: fix iteration in collapse_file
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-khugepaged-fix-iteration-in-collapse_file.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-fix-iteration-in-collapse_file.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Stevens <stevensd@xxxxxxxxxxxx>
Subject: mm/khugepaged: fix iteration in collapse_file
Date: Wed, 7 Jun 2023 14:31:35 +0900
Remove an unnecessary call to xas_set(index) when iterating over the
target range in collapse_file. The extra call to xas_set reset the xas
cursor to the top of the tree, causing the xas_next call on the next
iteration to walk the tree to index instead of advancing to index+1. This
returned the same page again, which would cause collapse_file to fail
because the page is already locked.
This bug was hidden when CONFIG_DEBUG_VM was set. When that config was
used, the xas_load in a subsequent VM_BUG_ON assert would walk xas from
the top of the tree to index, causing the xas_next call on the next loop
iteration to advance the cursor as expected.
Link: https://lkml.kernel.org/r/20230607053135.2087354-1-stevensd@xxxxxxxxxx
Fixes: a2e17cc2efc7 ("mm/khugepaged: maintain page cache uptodate flag")
Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Cc: Kirill A . Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 1 -
1 file changed, 1 deletion(-)
--- a/mm/khugepaged.c~mm-khugepaged-fix-iteration-in-collapse_file
+++ a/mm/khugepaged.c
@@ -2070,7 +2070,6 @@ static int collapse_file(struct mm_struc
TTU_IGNORE_MLOCK | TTU_BATCH_FLUSH);
xas_lock_irq(&xas);
- xas_set(&xas, index);
VM_BUG_ON_PAGE(page != xas_load(&xas), page);
_
Patches currently in -mm which might be from stevensd@xxxxxxxxxxxx are
mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch
mm-khugepaged-fix-iteration-in-collapse_file.patch
