| Message ID | 20191031012151.2722280-1-guro@fb.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly | expand |
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@fb.com> 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@fb.com> > > Reviewed-by: Shakeel Butt <shakeelb@google.com> > > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > > Cc: Daniel Jordan <daniel.m.jordan@oracle.com> > > 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
On Thu, Oct 31, 2019 at 09:38:40AM +0000, Naoya Horiguchi wrote: > 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@fb.com> 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@fb.com> > > > Reviewed-by: Shakeel Butt <shakeelb@google.com> > > > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > > > Cc: Daniel Jordan <daniel.m.jordan@oracle.com> > > > > 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. I agree. Thanks!
On Wed, 30 Oct 2019, Roman Gushchin 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@fb.com> > Reviewed-by: Shakeel Butt <shakeelb@google.com> > Cc: Vladimir Davydov <vdavydov.dev@gmail.com> > Cc: Daniel Jordan <daniel.m.jordan@oracle.com> Acked-by: David Rientjes <rientjes@google.com>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ea085877c548..00b4188b1bed 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -476,7 +476,7 @@ ino_t page_cgroup_ino(struct page *page) unsigned long ino = 0; rcu_read_lock(); - if (PageHead(page) && PageSlab(page)) + if (PageSlab(page) && !PageTail(page)) memcg = memcg_from_slab_page(page); else memcg = READ_ONCE(page->mem_cgroup); diff --git a/mm/slab.h b/mm/slab.h index 3eb29ae75743..8b77f973a6ab 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -323,8 +323,8 @@ static inline struct kmem_cache *memcg_root_cache(struct kmem_cache *s) * Expects a pointer to a slab page. Please note, that PageSlab() check * isn't sufficient, as it returns true also for tail compound slab pages, * which do not have slab_cache pointer set. - * So this function assumes that the page can pass PageHead() and PageSlab() - * checks. + * So this function assumes that the page can pass PageSlab() && !PageTail() + * check. * * The kmem_cache can be reparented asynchronously. The caller must ensure * the memcg lifetime, e.g. by taking rcu_read_lock() or cgroup_mutex.
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@fb.com> Reviewed-by: Shakeel Butt <shakeelb@google.com> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: Daniel Jordan <daniel.m.jordan@oracle.com> --- mm/memcontrol.c | 2 +- mm/slab.h | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-)