linux-kernel - [PATCH] vmscan: fix memcg

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Date:   Mon,  8 Jul 2019 14:41:03 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Arnd Bergmann <arnd@...db.de>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Hugh Dickins <hughd@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Roman Gushchin <guro@...com>,
        Chris Down <chris@...isdown.name>,
        Yafang Shao <laoar.shao@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH] vmscan: fix memcg_kmem build failure

When CONFIG_MEMCG_KMEM is disabled, we get a build failure
for calling a nonexisting memcg_expand_shrinker_maps():

mm/vmscan.c:220:7: error: implicit declaration of function 'memcg_expand_shrinker_maps' [-Werror,-Wimplicit-function-declaration]
                if (memcg_expand_shrinker_maps(id)) {
                    ^
mm/vmscan.c:220:7: error: this function declaration is not a prototype [-Werror,-Wstrict-prototypes]
mm/vmscan.c:608:56: error: no member named 'shrinker_map' in 'struct mem_cgroup_per_node'
        map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
                                        ~~~~~~~~~~~~~~~~~~~~  ^
include/linux/rcupdate.h:498:31: note: expanded from macro 'rcu_dereference_protected'
        __rcu_dereference_protected((p), (c), __rcu)
                                     ^
include/linux/rcupdate.h:321:12: note: expanded from macro '__rcu_dereference_protected'
        ((typeof(*p) __force __kernel *)(p)); \
                  ^
mm/vmscan.c:608:6: error: assigning to 'struct memcg_shrinker_map *' from incompatible type 'void'
        map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,

and another issue trying to access invalid struct fields:

mm/vmscan.c:608:56: error: no member named 'shrinker_map' in 'struct mem_cgroup_per_node'
        map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,
                                        ~~~~~~~~~~~~~~~~~~~~  ^
include/linux/rcupdate.h:498:31: note: expanded from macro 'rcu_dereference_protected'
        __rcu_dereference_protected((p), (c), __rcu)
                                     ^
include/linux/rcupdate.h:321:12: note: expanded from macro '__rcu_dereference_protected'
        ((typeof(*p) __force __kernel *)(p)); \
                  ^
mm/vmscan.c:608:6: error: assigning to 'struct memcg_shrinker_map *' from incompatible type 'void'
        map = rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_map,

Add a dummy definition for memcg_expand_shrinker_maps() that always fails,
and hide the obviously nonworking shrink_slab_memcg() function.

Fixes: 8236f517d69e ("mm: shrinker: make shrinker not depend on memcg kmem")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
No idea what the intended behavior is supposed to be for this case.
Rather than failing, should we actually provide that function?
Or maybe a more elaborate change is needed?
---
 include/linux/memcontrol.h | 5 +++++
 mm/vmscan.c                | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 5901a90f58eb..6b15e2066fc7 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1407,6 +1407,11 @@ static inline void memcg_put_cache_ids(void)
 {
 }
 
+static inline int memcg_expand_shrinker_maps(int new_id)
+{
+	return -ENOMEM;
+}
+
 static inline void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
 					  int nid, int shrinker_id) { }
 #endif /* CONFIG_MEMCG_KMEM */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index a0301edd8d03..323a9c50c0fe 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -591,7 +591,7 @@ static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
 	return freed;
 }
 
-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_KMEM
 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
 			struct mem_cgroup *memcg, int priority)
 {
-- 
2.20.0