[PATCH 5.2 379/413] mm/z3fold.c: lock z3fold page before __SetPageMovable()

[Greg Kroah-Hartman]

From: Henry Burns <henryburns@xxxxxxxxxx>

commit 810481a246089117d98e3373a3cb735c3efc1f90 upstream.

Following zsmalloc.c's example we call trylock_page() and unlock_page().
Also make z3fold_page_migrate() assert that newpage is passed in locked,
as per the documentation.

[akpm@xxxxxxxxxxxxxxxxxxxx: fix trylock_page return value test, per Shakeel]
Link: http://lkml.kernel.org/r/20190702005122.41036-1-henryburns@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20190702233538.52793-1-henryburns@xxxxxxxxxx
Signed-off-by: Henry Burns <henryburns@xxxxxxxxxx>
Suggested-by: Vitaly Wool <vitalywool@xxxxxxxxx>
Acked-by: Vitaly Wool <vitalywool@xxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Vitaly Vul <vitaly.vul@xxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Xidong Wang <wangxidong_97@xxxxxxx>
Cc: Jonathan Adams <jwadams@xxxxxxxxxx>
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/z3fold.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -924,7 +924,16 @@ retry:
 		set_bit(PAGE_HEADLESS, &page->private);
 		goto headless;
 	}
-	__SetPageMovable(page, pool->inode->i_mapping);
+	if (can_sleep) {
+		lock_page(page);
+		__SetPageMovable(page, pool->inode->i_mapping);
+		unlock_page(page);
+	} else {
+		if (trylock_page(page)) {
+			__SetPageMovable(page, pool->inode->i_mapping);
+			unlock_page(page);
+		}
+	}
 	z3fold_page_lock(zhdr);
 
 found:
@@ -1331,6 +1340,7 @@ static int z3fold_page_migrate(struct ad
 
 	VM_BUG_ON_PAGE(!PageMovable(page), page);
 	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
 	zhdr = page_address(page);
 	pool = zhdr_to_pool(zhdr);