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Subject[PATCH v2] mm/z3fold.c: Lock z3fold page before __SetPageMovable()
From
__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 <henryburns@google.com>
Suggested-by: Vitaly Wool <vitalywool@gmail.com>
---
Changelog since v1:
- Added an if statement around WARN_ON(trylock_page(page)) to avoid
unlocking a page locked by a someone else.

mm/z3fold.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index e174d1549734..6341435b9610 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -918,7 +918,10 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
set_bit(PAGE_HEADLESS, &page->private);
goto headless;
}
- __SetPageMovable(page, pool->inode->i_mapping);
+ if (!WARN_ON(!trylock_page(page))) {
+ __SetPageMovable(page, pool->inode->i_mapping);
+ unlock_page(page);
+ }
z3fold_page_lock(zhdr);

found:
@@ -1325,6 +1328,7 @@ 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
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