+ mm-khugepaged-fix-iteration-in-collapse_file.patch added to mm-hotfixes-unstable branch

+ mm-khugepaged-fix-iteration-in-collapse_file.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

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@chromium.org>
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@google.com
Fixes: a2e17cc2efc7 ("mm/khugepaged: maintain page cache uptodate flag")
Signed-off-by: David Stevens <stevensd@chromium.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Kirill A . Shutemov <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@chromium.org are

mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch
mm-khugepaged-fix-iteration-in-collapse_file.patch