[merged] mmthp-recheck-each-page-before-collapsing-file-thp.patch removed from -mm tree

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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 it was merged into mainline or a subsystem tree

------------------------------------------------------
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

mm-thp-flush-file-for-is_shmem-pagedirty-case-in-collapse_file.patch




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