diff mbox series

[1/2,v2] mm/zsmalloc.c: Migration can leave pages in ZS_EMPTY indefinitely

Message ID 20190809181751.219326-1-henryburns@google.com (mailing list archive)
State New, archived
Headers show
Series [1/2,v2] mm/zsmalloc.c: Migration can leave pages in ZS_EMPTY indefinitely | expand

Commit Message

Henry Burns Aug. 9, 2019, 6:17 p.m. UTC 
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@google.com>
---
 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(-)

Comments

Sergey Senozhatsky Aug. 20, 2019, 2:53 a.m. UTC | #1 
On (08/09/19 11:17), Henry Burns wrote:
> 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@google.com>

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

+ Andrew

	-ss
diff mbox series

Patch

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);
 }