From: Henry Burns henryburns@google.com Subject: mm/zsmalloc.c: migration can leave pages in ZS_EMPTY indefinitely

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: 48b4800a1c6a ("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 ---

mm/zsmalloc.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)

--- a/mm/zsmalloc.c~mm-zsmallocc-migration-can-leave-pages-in-zs_empty-indefinitely +++ a/mm/zsmalloc.c @@ -1862,6 +1862,18 @@ static void dec_zspage_isolation(struct 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 addres * 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 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); }

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