The patch titled
Subject: mm,thp: recheck each page before collapsing file THP
has been removed from the -mm tree. Its filename was
mmthp-recheck-each-page-before-collapsing-file-thp.patch
This patch was dropped because an updated version will be merged
------------------------------------------------------
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
only collapse read-only .text. Therefore, the page could only be dirty if
it hasn't been flushed since first write. In such case, calls
filemap_flush() and defer the collapse.
[songliubraving@xxxxxx: flush file for !is_shmem PageDirty() case in collapse_file()]
Link: http://lkml.kernel.org/r/20191030200736.3455046-1-songliubraving@xxxxxx
[songliubraving@xxxxxx: v4]
Link: http://lkml.kernel.org/r/20191022191006.411277-1-songliubraving@xxxxxx
[songliubraving@xxxxxx: fix deadlock in collapse_file()]
Link: http://lkml.kernel.org/r/20191028221414.3685035-1-songliubraving@xxxxxx
Link: http://lkml.kernel.org/r/20191018180345.4188310-1-songliubraving@xxxxxx
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Song Liu <songliubraving@xxxxxx>
Acked-by: 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 | 49 +++++++++++++++++++++++++++++++++++++---------
1 file changed, 40 insertions(+), 9 deletions(-)
--- a/mm/khugepaged.c~mmthp-recheck-each-page-before-collapsing-file-thp
+++ a/mm/khugepaged.c
@@ -1601,17 +1601,33 @@ 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;
+ if (WARN_ON_ONCE(PageDirty(page))) {
+ /*
+ * page from readahead should not
+ * be dirty. Show warning if this
+ * somehow happens.
+ */
+ result = SCAN_FAIL;
+ goto out_unlock;
}
- get_page(page);
} else if (PageDirty(page)) {
+ /*
+ * khugepaged only works on read-only fd,
+ * so this page is dirty because it hasn't
+ * been flushed since first write. There
+ * won't be new dirty pages.
+ *
+ * Trigger async flush here and hope the
+ * writeback is done when khugepaged
+ * revisits this page.
+ *
+ * This is a one-off situation. We are not
+ * forcing writeback in loop.
+ */
+ xas_unlock_irq(&xas);
+ filemap_flush(mapping);
result = SCAN_FAIL;
- goto xa_locked;
+ goto xa_unlocked;
} else if (trylock_page(page)) {
get_page(page);
xas_unlock_irq(&xas);
@@ -1626,7 +1642,12 @@ 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);
+
+ /* double check 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
@@ -1642,6 +1663,16 @@ 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
maintainers-update-information-for-memory-management.patch
