Commit b8529907 authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
Browse files

memcg, slab: do not destroy children caches if parent has aliases



Currently we destroy children caches at the very beginning of
kmem_cache_destroy().  This is wrong, because the root cache will not
necessarily be destroyed in the end - if it has aliases (refcount > 0),
kmem_cache_destroy() will simply decrement its refcount and return.  In
this case, at best we will get a bunch of warnings in dmesg, like this
one:

  kmem_cache_destroy kmalloc-32:0: Slab cache still has objects
  CPU: 1 PID: 7139 Comm: modprobe Tainted: G    B   W    3.13.0+ #117
  Call Trace:
    dump_stack+0x49/0x5b
    kmem_cache_destroy+0xdf/0xf0
    kmem_cache_destroy_memcg_children+0x97/0xc0
    kmem_cache_destroy+0xf/0xf0
    xfs_mru_cache_uninit+0x21/0x30 [xfs]
    exit_xfs_fs+0x2e/0xc44 [xfs]
    SyS_delete_module+0x198/0x1f0
    system_call_fastpath+0x16/0x1b

At worst - if kmem_cache_destroy() will race with an allocation from a
memcg cache - the kernel will panic.

This patch fixes this by moving children caches destruction after the
check if the cache has aliases.  Plus, it forbids destroying a root
cache if it still has children caches, because each children cache keeps
a reference to its parent.
Signed-off-by: default avatarVladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Glauber Costa <glommer@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 051dd460
......@@ -507,7 +507,7 @@ struct kmem_cache *
__memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp);
void mem_cgroup_destroy_cache(struct kmem_cache *cachep);
void kmem_cache_destroy_memcg_children(struct kmem_cache *s);
int __kmem_cache_destroy_memcg_children(struct kmem_cache *s);
/**
* memcg_kmem_newpage_charge: verify if a new kmem allocation is allowed.
......@@ -661,10 +661,6 @@ memcg_kmem_get_cache(struct kmem_cache *cachep, gfp_t gfp)
{
return cachep;
}
static inline void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
{
}
#endif /* CONFIG_MEMCG_KMEM */
#endif /* _LINUX_MEMCONTROL_H */
......@@ -3321,15 +3321,10 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
schedule_work(&cachep->memcg_params->destroy);
}
void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
int __kmem_cache_destroy_memcg_children(struct kmem_cache *s)
{
struct kmem_cache *c;
int i;
if (!s->memcg_params)
return;
if (!s->memcg_params->is_root_cache)
return;
int i, failed = 0;
/*
* If the cache is being destroyed, we trust that there is no one else
......@@ -3363,8 +3358,12 @@ void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
c->memcg_params->dead = false;
cancel_work_sync(&c->memcg_params->destroy);
kmem_cache_destroy(c);
if (cache_from_memcg_idx(s, i))
failed++;
}
mutex_unlock(&activate_kmem_mutex);
return failed;
}
static void mem_cgroup_destroy_all_caches(struct mem_cgroup *memcg)
......
......@@ -301,39 +301,64 @@ out_unlock:
mutex_unlock(&slab_mutex);
put_online_cpus();
}
static int kmem_cache_destroy_memcg_children(struct kmem_cache *s)
{
int rc;
if (!s->memcg_params ||
!s->memcg_params->is_root_cache)
return 0;
mutex_unlock(&slab_mutex);
rc = __kmem_cache_destroy_memcg_children(s);
mutex_lock(&slab_mutex);
return rc;
}
#else
static int kmem_cache_destroy_memcg_children(struct kmem_cache *s)
{
return 0;
}
#endif /* CONFIG_MEMCG_KMEM */
void kmem_cache_destroy(struct kmem_cache *s)
{
/* Destroy all the children caches if we aren't a memcg cache */
kmem_cache_destroy_memcg_children(s);
get_online_cpus();
mutex_lock(&slab_mutex);
s->refcount--;
if (!s->refcount) {
list_del(&s->list);
memcg_unregister_cache(s);
if (!__kmem_cache_shutdown(s)) {
mutex_unlock(&slab_mutex);
if (s->flags & SLAB_DESTROY_BY_RCU)
rcu_barrier();
memcg_free_cache_params(s);
kfree(s->name);
kmem_cache_free(kmem_cache, s);
} else {
list_add(&s->list, &slab_caches);
memcg_register_cache(s);
mutex_unlock(&slab_mutex);
printk(KERN_ERR "kmem_cache_destroy %s: Slab cache still has objects\n",
s->name);
dump_stack();
}
} else {
mutex_unlock(&slab_mutex);
if (s->refcount)
goto out_unlock;
if (kmem_cache_destroy_memcg_children(s) != 0)
goto out_unlock;
list_del(&s->list);
memcg_unregister_cache(s);
if (__kmem_cache_shutdown(s) != 0) {
list_add(&s->list, &slab_caches);
memcg_register_cache(s);
printk(KERN_ERR "kmem_cache_destroy %s: "
"Slab cache still has objects\n", s->name);
dump_stack();
goto out_unlock;
}
mutex_unlock(&slab_mutex);
if (s->flags & SLAB_DESTROY_BY_RCU)
rcu_barrier();
memcg_free_cache_params(s);
kfree(s->name);
kmem_cache_free(kmem_cache, s);
goto out_put_cpus;
out_unlock:
mutex_unlock(&slab_mutex);
out_put_cpus:
put_online_cpus();
}
EXPORT_SYMBOL(kmem_cache_destroy);
......
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