This is a note to let you know that I've just added the patch titled
mm/khugepaged.c: convert VM_BUG_ON() to collapse fail
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-khugepaged.c-convert-vm_bug_on-to-collapse-fail.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From fece2029a9e65b9a990831afe2a2b83290cbbe26 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Thu, 22 Mar 2018 16:17:28 -0700
Subject: mm/khugepaged.c: convert VM_BUG_ON() to collapse fail
From: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
commit fece2029a9e65b9a990831afe2a2b83290cbbe26 upstream.
khugepaged is not yet able to convert PTE-mapped huge pages back to PMD
mapped. We do not collapse such pages. See check
khugepaged_scan_pmd().
But if between khugepaged_scan_pmd() and __collapse_huge_page_isolate()
somebody managed to instantiate THP in the range and then split the PMD
back to PTEs we would have a problem --
VM_BUG_ON_PAGE(PageCompound(page)) will get triggered.
It's possible since we drop mmap_sem during collapse to re-take for
write.
Replace the VM_BUG_ON() with graceful collapse fail.
Link: http://lkml.kernel.org/r/20180315152353.27989-1-kirill.shutemov@xxxxxxxxxxxxxxx
Fixes: b1caa957ae6d ("khugepaged: ignore pmd tables with THP mapped with ptes")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Jerome Marchand <jmarchan@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -528,7 +528,12 @@ static int __collapse_huge_page_isolate(
goto out;
}
- VM_BUG_ON_PAGE(PageCompound(page), page);
+ /* TODO: teach khugepaged to collapse THP mapped with pte */
+ if (PageCompound(page)) {
+ result = SCAN_PAGE_COMPOUND;
+ goto out;
+ }
+
VM_BUG_ON_PAGE(!PageAnon(page), page);
VM_BUG_ON_PAGE(!PageSwapBacked(page), page);
Patches currently in stable-queue which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
queue-4.9/mm-khugepaged.c-convert-vm_bug_on-to-collapse-fail.patch
queue-4.9/mm-thp-do-not-wait-for-lock_page-in-deferred_split_scan.patch
queue-4.9/mm-shmem-do-not-wait-for-lock_page-in-shmem_unused_huge_shrink.patch