On Wed, Oct 30, 2019 at 09:16:08PM -0700, Andrew Morton wrote:
> On Wed, 30 Oct 2019 18:21:51 -0700 Roman Gushchin <guro@xxxxxx> wrote:
>
> > page_cgroup_ino() doesn't return a valid memcg pointer for non-compound
> > slab pages, because it depends on PgHead AND PgSlab flags to be set
> > to determine the memory cgroup from the kmem_cache.
> > It's correct for compound pages, but not for generic small pages. Those
> > don't have PgHead set, so it ends up returning zero.
> >
> > Fix this by replacing the condition to PageSlab() && !PageTail().
> >
> > Before this patch:
> > [root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@0.service/ | grep slab
> > 0x0000000000000080 38 0 _______S___________________________________ slab
> >
> > After this patch:
> > [root@localhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@0.service/ | grep slab
> > 0x0000000000000080 147 0 _______S___________________________________ slab
> >
> > Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
> > Signed-off-by: Roman Gushchin <guro@xxxxxx>
> > Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> > Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
> > Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
>
> Affects /proc/kpagecgroup, but page_cgroup_ino() is also used in the
> memory-failure code - I wonder what effect this bug has there?
hwpoison_filter_task() uses output of page_cgroup_ino() in order to
filter error injection events based on memcg.
So if page_cgroup_ino() fails to return memcg pointer, we just fail
to inject memory error. Considering that hwpoison filter is for testing,
affected users are limited and the impact should be marginal.
>
> IOW, should we backport this into -stable?
I think yes, because the patch is small enough and clearly fixes a bug.
Thanks,
Naoya Horiguchi
