Commit b30a2f60 authored Aug 24, 2019 by Henry Burns Committed by Greg Kroah-Hartman Aug 29, 2019

mm/zsmalloc.c: migration can leave pages in ZS_EMPTY indefinitely

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@google.com


Fixes: 48b4800a ("zsmalloc: page migration support")
Signed-off-by: Henry Burns <henryburns@google.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Jonathan Adams <jwadams@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent db67ac03

mm/zsmalloc.c

+15 −4

Original line number	Diff line number	Diff line
		@@ -1882,6 +1882,18 @@ 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)
		{
		@@ -2051,7 +2063,7 @@ 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);
		@@ -2097,14 +2109,13 @@ 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);
		}