[PATCH] mm/z3fold.c: Lock z3fold page before __SetPageMovable()

[Henry Burns]

__SetPageMovable() expects it's page to be locked, but z3fold.c doesn't
lock the page. Following zsmalloc.c's example we call trylock_page() and
unlock_page(). Also makes z3fold_page_migrate() assert that newpage is
passed in locked, as documentation.

Signed-off-by: Henry Burns <henrybu...@google.com>
---
 mm/z3fold.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index e174d1549734..5bc404dbbb4a 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -918,7 +918,9 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t 
size, gfp_t gfp,
                set_bit(PAGE_HEADLESS, &page->private);
                goto headless;
        }
+       WARN_ON(!trylock_page(page));
        __SetPageMovable(page, pool->inode->i_mapping);
+       unlock_page(page);
        z3fold_page_lock(zhdr);
 
 found:
@@ -1325,6 +1327,7 @@ static int z3fold_page_migrate(struct address_space 
*mapping, struct page *newpa
 
        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);
-- 
2.22.0.410.gd8fdbe21b5-goog