[PATCH 4.14 58/62] mm/zsmalloc.c: migration can leave pages in ZS_EMPTY indefinitely

From: Greg Kroah-Hartman
Date: Tue Aug 27 2019 - 03:54:37 EST

From: Henry Burns <henryburns@xxxxxxxxxx>

commit 1a87aa03597efa9641e92875b883c94c7f872ccb upstream.

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.

Link: http://lkml.kernel.org/r/20190809181751.219326-1-henryburns@xxxxxxxxxx
Fixes: 48b4800a1c6a ("zsmalloc: page migration support")
Signed-off-by: Henry Burns <henryburns@xxxxxxxxxx>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
Cc: Henry Burns <henrywolfeburns@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
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/zsmalloc.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -1878,6 +1878,18 @@ static void dec_zspage_isolation(struct

+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)
@@ -2047,7 +2059,7 @@ int zs_page_migrate(struct address_space
* 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);

@@ -2093,14 +2105,13 @@ void zs_page_putback(struct page *page)
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);