On Thu, Aug 01, 2019 at 06:53:31PM -0700, 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.
Nice catch.
>
> 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.
>
> Signed-off-by: Henry Burns <henryburns@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.8+]
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Below a just trivial:
> ---
> mm/zsmalloc.c | 30 ++++++++++++++++++++----------
> 1 file changed, 20 insertions(+), 10 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 1cda3fe0c2d9..efa660a87787 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1901,6 +1901,22 @@ 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);
> + /*
> + * Due to page_lock, we cannot free zspage immediately
> + * so let's defer.
> + */
Could you move this comment function's description since it becomes
a function?
Thanks.
