[060/155] mm, memcg: fix build error around the usage of kmem_caches

Commit Message

Andrew Morton April 2, 2020, 4:06 a.m. UTC

From: Yafang Shao <[e-mail]>
Subject: mm, memcg: fix build error around the usage of kmem_caches

When I manually set default n to MEMCG_KMEM in init/Kconfig, bellow error
occurs,

mm/slab_common.c: In function 'memcg_slab_start':
mm/slab_common.c:1530:30: error: 'struct mem_cgroup' has no member named
'kmem_caches'
  return seq_list_start(&memcg->kmem_caches, *pos);
                              ^
mm/slab_common.c: In function 'memcg_slab_next':
mm/slab_common.c:1537:32: error: 'struct mem_cgroup' has no member named
'kmem_caches'
  return seq_list_next(p, &memcg->kmem_caches, pos);
                                ^
mm/slab_common.c: In function 'memcg_slab_show':
mm/slab_common.c:1551:16: error: 'struct mem_cgroup' has no member named
'kmem_caches'
  if (p == memcg->kmem_caches.next)
                ^
  CC      arch/x86/xen/smp.o
mm/slab_common.c: In function 'memcg_slab_start':
mm/slab_common.c:1531:1: warning: control reaches end of non-void function
[-Wreturn-type]
 }
 ^
mm/slab_common.c: In function 'memcg_slab_next':
mm/slab_common.c:1538:1: warning: control reaches end of non-void function
[-Wreturn-type]
 }
 ^

That's because kmem_caches is defined only when CONFIG_MEMCG_KMEM is set,
while memcg_slab_start() will use it no matter CONFIG_MEMCG_KMEM is defined
or not.

By the way, the reason I mannuly undefined CONFIG_MEMCG_KMEM is to verify
whether my some other code change is still stable when CONFIG_MEMCG_KMEM is
not set. Unfortunately, the existing code has been already unstable since
v4.11.

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: bc2791f857e1 ("slab: link memcg kmem_caches on their associated memory cgroup")
Signed-off-by: Yafang Shao <[e-mail]>
Acked-by: Andrew Morton <[e-mail]>
Cc: Tejun Heo <[e-mail]>
Cc: Vladimir Davydov <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

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

Patch

--- a/mm/memcontrol.c~mm-memcg-fix-build-error-around-the-usage-of-kmem_caches
+++ a/mm/memcontrol.c
@@ -4792,7 +4792,8 @@  static struct cftype mem_cgroup_legacy_f
 		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
-#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
+#if defined(CONFIG_MEMCG_KMEM) && \
+	(defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG))
 	{
 		.name = "kmem.slabinfo",
 		.seq_start = memcg_slab_start,
--- a/mm/slab_common.c~mm-memcg-fix-build-error-around-the-usage-of-kmem_caches
+++ a/mm/slab_common.c
@@ -1521,7 +1521,7 @@  void dump_unreclaimable_slab(void)
 	mutex_unlock(&slab_mutex);
 }
 
-#if defined(CONFIG_MEMCG)
+#if defined(CONFIG_MEMCG_KMEM)
 void *memcg_slab_start(struct seq_file *m, loff_t *pos)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);