release/5.2.58/mm-memcg-slab-synchronize-access-to-kmem_cache-dying.patch

From 443801ac41eb42cac2c4fbae3a4e5e814fe377aa Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Thu, 11 Jul 2019 20:56:24 -0700
Subject: [PATCH] mm: memcg/slab: synchronize access to kmem_cache dying flag
 using a spinlock

commit 63b02ef7dc4ec239df45c018ac0adbd02ba30a0c upstream.

Currently the memcg_params.dying flag and the corresponding workqueue used
for the asynchronous deactivation of kmem_caches is synchronized using the
slab_mutex.

It makes impossible to check this flag from the irq context, which will be
required in order to implement asynchronous release of kmem_caches.

So let's switch over to the irq-save flavor of the spinlock-based
synchronization.

Link: http://lkml.kernel.org/r/20190611231813.3148843-8-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Vladimir Davydov <vdavydov.dev@gmail.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Waiman Long <longman@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 0d247ef3057b..70fb7eec7360 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -130,6 +130,7 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t nr,
 #ifdef CONFIG_MEMCG_KMEM
 
 LIST_HEAD(slab_root_caches);
+static DEFINE_SPINLOCK(memcg_kmem_wq_lock);
 
 void slab_init_memcg_params(struct kmem_cache *s)
 {
@@ -752,14 +753,22 @@ void slab_deactivate_memcg_cache_rcu_sched(struct kmem_cache *s,
 	    WARN_ON_ONCE(s->memcg_params.deact_fn))
 		return;
 
+	/*
+	 * memcg_kmem_wq_lock is used to synchronize memcg_params.dying
+	 * flag and make sure that no new kmem_cache deactivation tasks
+	 * are queued (see flush_memcg_workqueue() ).
+	 */
+	spin_lock_irq(&memcg_kmem_wq_lock);
 	if (s->memcg_params.root_cache->memcg_params.dying)
-		return;
+		goto unlock;
 
 	/* pin memcg so that @s doesn't get destroyed in the middle */
 	css_get(&s->memcg_params.memcg->css);
 
 	s->memcg_params.deact_fn = deact_fn;
 	call_rcu(&s->memcg_params.deact_rcu_head, kmemcg_deactivate_rcufn);
+unlock:
+	spin_unlock_irq(&memcg_kmem_wq_lock);
 }
 
 void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
@@ -869,9 +878,9 @@ static int shutdown_memcg_caches(struct kmem_cache *s)
 
 static void memcg_set_kmem_cache_dying(struct kmem_cache *s)
 {
-	mutex_lock(&slab_mutex);
+	spin_lock_irq(&memcg_kmem_wq_lock);
 	s->memcg_params.dying = true;
-	mutex_unlock(&slab_mutex);
+	spin_unlock_irq(&memcg_kmem_wq_lock);
 }
 
 static void flush_memcg_workqueue(struct kmem_cache *s)
-- 
2.27.0