The patch titled
Subject: mm,thp: recheck each page before collapsing file THP
has been added to the -mm tree. Its filename is
mmthp-recheck-each-page-before-collapsing-file-thp.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmthp-recheck-each-page-before-collapsing-file-thp.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmthp-recheck-each-page-before-collapsing-file-thp.patch
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------------------------------------------------------
From: Song Liu <songliubraving@xxxxxx>
Subject: mm,thp: recheck each page before collapsing file THP
In collapse_file(), for !is_shmem case, current check cannot guarantee the
locked page is up-to-date. Specifically, xas_unlock_irq() should not be
called before lock_page() and get_page(); and it is necessary to recheck
PageUptodate() after locking the page.
With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text
may contain corrupted data. This is because khugepaged mistakenly
collapses some not up-to-date sub pages into a huge page, and assumes the
huge page is up-to-date. This will NOT corrupt data in the disk, because
the page is read-only and never written back. Fix this by properly
checking PageUptodate() after locking the page. This check replaces
"VM_BUG_ON_PAGE(!PageUptodate(page), page);".
Also, move PageDirty() check after locking the page. Current khugepaged
should not try to collapse dirty file THP, because it is limited to
read-only .text. The only case we hit a dirty page here is when the page
hasn't been written since write. Bail out and retry when this happens.
syzbot reported bug on previous version of this patch.
Link: http://lkml.kernel.org/r/20191106060930.2571389-2-songliubraving@xxxxxx
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Reported-by: syzbot+efb9e48b9fbdc49bb34a@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)
--- a/mm/khugepaged.c~mmthp-recheck-each-page-before-collapsing-file-thp
+++ a/mm/khugepaged.c
@@ -1602,17 +1602,6 @@ static void collapse_file(struct mm_stru
result = SCAN_FAIL;
goto xa_unlocked;
}
- } else if (!PageUptodate(page)) {
- xas_unlock_irq(&xas);
- wait_on_page_locked(page);
- if (!trylock_page(page)) {
- result = SCAN_PAGE_LOCK;
- goto xa_unlocked;
- }
- get_page(page);
- } else if (PageDirty(page)) {
- result = SCAN_FAIL;
- goto xa_locked;
} else if (trylock_page(page)) {
get_page(page);
xas_unlock_irq(&xas);
@@ -1627,7 +1616,12 @@ static void collapse_file(struct mm_stru
* without racing with truncate.
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);
- VM_BUG_ON_PAGE(!PageUptodate(page), page);
+
+ /* make sure the page is up to date */
+ if (unlikely(!PageUptodate(page))) {
+ result = SCAN_FAIL;
+ goto out_unlock;
+ }
/*
* If file was truncated then extended, or hole-punched, before
@@ -1643,6 +1637,16 @@ static void collapse_file(struct mm_stru
goto out_unlock;
}
+ if (!is_shmem && PageDirty(page)) {
+ /*
+ * khugepaged only works on read-only fd, so this
+ * page is dirty because it hasn't been flushed
+ * since first write.
+ */
+ result = SCAN_FAIL;
+ goto out_unlock;
+ }
+
if (isolate_lru_page(page)) {
result = SCAN_DEL_PAGE_LRU;
goto out_unlock;
_
Patches currently in -mm which might be from songliubraving@xxxxxx are
mmthp-recheck-each-page-before-collapsing-file-thp.patch
mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch
