linux-kernel - [PATCH 5.3 034/193] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

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Date:   Mon, 11 Nov 2019 19:26:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.3 034/193] mm: slab: make page_cgroup_ino() to recognize non-compound slab pages properly

From: Roman Gushchin <guro@...com>

commit 221ec5c0a46c1a1740f34fb36fc661a5284d01b0 upstream.

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@...alhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@...ervice/ | grep slab
  0x0000000000000080	        38        0  _______S___________________________________	slab

After this patch:
  [root@...alhost ~]# ./page-types -c /sys/fs/cgroup/user.slice/user-0.slice/user@...ervice/ | 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@...jp.nec.com: changelog additions]
Link: http://lkml.kernel.org/r/20191031012151.2722280-1-guro@fb.com
Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages")
Signed-off-by: Roman Gushchin <guro@...com>
Reviewed-by: Shakeel Butt <shakeelb@...gle.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>
Cc: Daniel Jordan <daniel.m.jordan@...cle.com>
Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/memcontrol.c |    2 +-
 mm/slab.h       |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -486,7 +486,7 @@ 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);
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -259,8 +259,8 @@ static inline struct kmem_cache *memcg_r
  * 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.