linux-kernel - Re: [PATCH] memcg: fix mutex not unlocked on memcg_create_kmem

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Date:	Thu, 30 Jan 2014 14:39:51 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Vladimir Davydov <vdavydov@...allels.com>, mhocko@...e.cz,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: fix mutex not unlocked on memcg_create_kmem_cache
 fail path

On Thu, 30 Jan 2014, Andrew Morton wrote:

> > It always was.
> 
> eh?  kmem_cache_create_memcg()'s kstrdup() will allocate the minimum
> needed amount of memory.
> 

Ah, good point.  We could this incrementally on my patch:

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -637,6 +637,9 @@ int memcg_limited_groups_array_size;
  * better kept as an internal representation in cgroup.c. In any case, the
  * cgrp_id space is not getting any smaller, and we don't have to necessarily
  * increase ours as well if it increases.
+ *
+ * Updates to MAX_SIZE should update the space for the memcg name in
+ * memcg_create_kmem_cache().
  */
 #define MEMCG_CACHES_MIN_SIZE 4
 #define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX
@@ -3400,8 +3403,10 @@ void mem_cgroup_destroy_cache(struct kmem_cache *cachep)
 static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 						  struct kmem_cache *s)
 {
-	char *name = NULL;
 	struct kmem_cache *new;
+	const char *cgrp_name;
+	char *name = NULL;
+	size_t len;
 
 	BUG_ON(!memcg_can_account_kmem(memcg));
 
@@ -3409,9 +3414,22 @@ static struct kmem_cache *memcg_create_kmem_cache(struct mem_cgroup *memcg,
 	if (unlikely(!name))
 		return NULL;
 
+	/*
+	 * Format of a memcg's kmem cache name:
+	 * <cache-name>(<memcg-id>:<cgroup-name>)
+	 */
+	len = strlen(s->name);
+	/* Space for parentheses, colon, terminator */
+	len += 4;
+	/* MEMCG_CACHES_MAX_SIZE is USHRT_MAX */
+	len += 5;
+	BUILD_BUG_ON(MEMCG_CACHES_MAX_SIZE > USHRT_MAX);
+
 	rcu_read_lock();
-	snprintf(name, PATH_MAX, "%s(%d:%s)", s->name, memcg_cache_id(memcg),
-		 cgroup_name(memcg->css.cgroup));
+	cgrp_name = cgroup_name(memcg->css.cgroup);
+	len += strlen(cgrp_name);
+	snprintf(name, len, "%s(%d:%s)", s->name, memcg_cache_id(memcg),
+		 cgrp_name);
 	rcu_read_unlock();
 
 	new = kmem_cache_create_memcg(memcg, name, s->object_size, s->align,
--
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