linux-kernel - [PATCH] slab: annotate on-slab caches nodelist locks

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Date:	Mon, 29 Oct 2012 14:49:39 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	<linux-mm@...ck.org>
Cc:	<linux-kernel@...r.kernel.org>,
	Glauber Costa <glommer@...allels.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	David Rientjes <rientjes@...gle.com>,
	JoonSoo Kim <js1304@...il.com>
Subject: [PATCH] slab: annotate on-slab caches nodelist locks

We currently provide lockdep annotation for kmalloc caches, and also
caches that have SLAB_DEBUG_OBJECTS enabled. The reason for this is that
we can quite frequently nest in the l3->list_lock lock, which is not
something trivial to avoid.

My proposal with this patch, is to extend this to caches whose slab
management object lives within the slab as well ("on_slab"). The need
for this arose in the context of testing kmemcg-slab patches. With such
patchset, we can have per-memcg kmalloc caches. So the same path that
led to nesting between kmalloc caches will could then lead to in-memcg
nesting. Because they are not annotated, lockdep will trigger.

Signed-off-by: Glauber Costa <glommer@...allels.com>
CC: Christoph Lameter <cl@...ux.com>
CC: Pekka Enberg <penberg@...helsinki.fi>
CC: David Rientjes <rientjes@...gle.com>
CC: JoonSoo Kim <js1304@...il.com>

---
Instead of "on_slab", I considered checking the memcg cache's root
cache, and annotating that only in case this is a kmalloc cache.
I ended up annotating on_slab caches, because given how frequently
those locks can nest, it seemed like a safe choice to go. I was
a little bit inspired by the key's name as well, that indicated
this could work for all on_slab caches. Let me know if you guys
want a different test condition for this.
---
 mm/slab.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/mm/slab.c b/mm/slab.c
index 9b7f6b63..ef1c8b3 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -654,6 +654,26 @@ static void init_node_lock_keys(int q)
 	}
 }
 
+static void on_slab_lock_classes_node(struct kmem_cache *cachep, int q)
+{
+	struct kmem_list3 *l3;
+	l3 = cachep->nodelists[q];
+	if (!l3)
+		return;
+
+	slab_set_lock_classes(cachep, &on_slab_l3_key,
+			&on_slab_alc_key, q);
+}
+
+static inline void on_slab_lock_classes(struct kmem_cache *cachep)
+{
+	int node;
+
+	VM_BUG_ON(OFF_SLAB(cachep));
+	for_each_node(node)
+		on_slab_lock_classes_node(cachep, node);
+}
+
 static inline void init_lock_keys(void)
 {
 	int node;
@@ -670,6 +690,10 @@ static inline void init_lock_keys(void)
 {
 }
 
+static inline void on_slab_lock_classes(struct kmem_cache *cachep)
+{
+}
+
 static void slab_set_debugobj_lock_classes_node(struct kmem_cache *cachep, int node)
 {
 }
@@ -1397,6 +1421,9 @@ static int __cpuinit cpuup_prepare(long cpu)
 		free_alien_cache(alien);
 		if (cachep->flags & SLAB_DEBUG_OBJECTS)
 			slab_set_debugobj_lock_classes_node(cachep, node);
+		else if (!OFF_SLAB(cachep) &&
+			 !(cachep->flags & SLAB_DESTROY_BY_RCU))
+			on_slab_lock_classes_node(cachep, node);
 	}
 	init_node_lock_keys(node);
 
@@ -2554,7 +2581,8 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
 		WARN_ON_ONCE(flags & SLAB_DESTROY_BY_RCU);
 
 		slab_set_debugobj_lock_classes(cachep);
-	}
+	} else if (!OFF_SLAB(cachep) && !(flags & SLAB_DESTROY_BY_RCU))
+		on_slab_lock_classes(cachep);
 
 	return 0;
 }
-- 
1.7.11.7

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