In zs_page_migrate() we call putback_zspage() after we have finished
migrating all pages in this zspage. However, the return value is ignored.
If a zs_free() races in between zs_page_isolate() and zs_page_migrate(),
freeing the last object in the zspage, putback_zspage() will leave the page
in ZS_EMPTY for potentially an unbounded amount of time.
To fix this, we need to do the same thing as zs_page_putback() does:
schedule free_work to occur. To avoid duplicated code, move the
sequence to a new putback_zspage_deferred() function which both
zs_page_migrate() and zs_page_putback() call.
Fixes: 48b4800a1c6a ("zsmalloc: page migration support")
Signed-off-by: Henry Burns <henryburns@xxxxxxxxxx>
---
Changelog since v1:
- Moved the comment from putback_zspage_deferred() to
zs_page_putback().
mm/zsmalloc.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 57fbb7ced69f..5105b9b66653 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1862,6 +1862,18 @@ static void dec_zspage_isolation(struct zspage *zspage)
zspage->isolated--;
}
+static void putback_zspage_deferred(struct zs_pool *pool,
+ struct size_class *class,
+ struct zspage *zspage)
+{
+ enum fullness_group fg;
+
+ fg = putback_zspage(class, zspage);
+ if (fg == ZS_EMPTY)
+ schedule_work(&pool->free_work);
+
+}
+
static void replace_sub_page(struct size_class *class, struct zspage *zspage,
struct page *newpage, struct page *oldpage)
{
@@ -2031,7 +2043,7 @@ static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
* the list if @page is final isolated subpage in the zspage.
*/
if (!is_zspage_isolated(zspage))
- putback_zspage(class, zspage);
+ putback_zspage_deferred(pool, class, zspage);
reset_page(page);
put_page(page);
@@ -2077,14 +2089,13 @@ static void zs_page_putback(struct page *page)
spin_lock(&class->lock);
dec_zspage_isolation(zspage);
if (!is_zspage_isolated(zspage)) {
- fg = putback_zspage(class, zspage);
/*
* Due to page_lock, we cannot free zspage immediately
* so let's defer.
*/
- if (fg == ZS_EMPTY)
- schedule_work(&pool->free_work);
+ putback_zspage_deferred(pool, class, zspage);
}
+
spin_unlock(&class->lock);
}
--
2.23.0.rc1.153.gdeed80330f-goog
