Commit 221ec5c0 authored Nov 05, 2019 by Roman Gushchin Committed by Linus Torvalds Nov 06, 2019

mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

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

Also, 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.

[n-horiguchi@ah.jp.nec.com: changelog additions]
Link: http://lkml.kernel.org/r/20191031012151.2722280-1-guro@fb.com


Fixes: 4d96ba35 ("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>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6981b76c

mm/memcontrol.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -484,7 +484,7 @@ 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);

mm/slab.h

+2 −2

Original line number	Diff line number	Diff line
		@@ -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.

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