Commit 83835b3d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

slab, lockdep: Annotate slab -> rcu -> debug_object -> slab 



Lockdep thinks there's lock recursion through:

	kmem_cache_free()
	  cache_flusharray()
	    spin_lock(&l3->list_lock)  <----------------.
	    free_block()                                |
	      slab_destroy()                            |
		call_rcu()                              |
		  debug_object_activate()               |
		    debug_object_init()                 |
		      __debug_object_init()             |
			kmem_cache_alloc()              |
			  cache_alloc_refill()          |
			    spin_lock(&l3->list_lock) --'

Now debug objects doesn't use SLAB_DESTROY_BY_RCU and hence there is no
actual possibility of recursing. Luckily debug objects marks it slab
with SLAB_DEBUG_OBJECTS so we can identify the thing.

Mark all SLAB_DEBUG_OBJECTS (all one!) slab caches with a special
lockdep key so that lockdep sees its a different cachep.

Also add a WARN on trying to create a SLAB_DESTROY_BY_RCU |
SLAB_DEBUG_OBJECTS cache, to avoid possible future trouble.

Reported-and-tested-by: default avatarSebastian Siewior <sebastian@breakpoint.cc>
[ fixes to the initial patch ]
Reported-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPekka Enberg <penberg@kernel.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1311341165.27400.58.camel@twins


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 70a0686a

mm/slab.c

+68 −18
Original line number Diff line number Diff line
@@ -622,22 +622,22 @@ int slab_is_available(void) 
static struct lock_class_key on_slab_l3_key;

static struct lock_class_key on_slab_alc_key;



static void init_node_lock_keys(int q)

{

	struct cache_sizes *s = malloc_sizes;

static struct lock_class_key debugobj_l3_key;

static struct lock_class_key debugobj_alc_key;



	if (g_cpucache_up != FULL)

		return;



	for (s = malloc_sizes; s->cs_size != ULONG_MAX; s++) {

static void slab_set_lock_classes(struct kmem_cache *cachep,

		struct lock_class_key *l3_key, struct lock_class_key *alc_key,

		int q)

{

	struct array_cache **alc;

	struct kmem_list3 *l3;

	int r;



		l3 = s->cs_cachep->nodelists[q];

		if (!l3 || OFF_SLAB(s->cs_cachep))

			continue;

		lockdep_set_class(&l3->list_lock, &on_slab_l3_key);

	l3 = cachep->nodelists[q];

	if (!l3)

		return;



	lockdep_set_class(&l3->list_lock, l3_key);

	alc = l3->alien;

	/*

	 * FIXME: This check for BAD_ALIEN_MAGIC
@@ -647,13 +647,43 @@ static void init_node_lock_keys(int q) 
	 * for alloc_alien_cache,

	 */

	if (!alc || (unsigned long)alc == BAD_ALIEN_MAGIC)

			continue;

		return;

	for_each_node(r) {

		if (alc[r])

				lockdep_set_class(&alc[r]->lock,

					&on_slab_alc_key);

			lockdep_set_class(&alc[r]->lock, alc_key);

	}

}



static void slab_set_debugobj_lock_classes_node(struct kmem_cache *cachep, int node)

{

	slab_set_lock_classes(cachep, &debugobj_l3_key, &debugobj_alc_key, node);

}



static void slab_set_debugobj_lock_classes(struct kmem_cache *cachep)

{

	int node;



	for_each_online_node(node)

		slab_set_debugobj_lock_classes_node(cachep, node);

}



static void init_node_lock_keys(int q)

{

	struct cache_sizes *s = malloc_sizes;



	if (g_cpucache_up != FULL)

		return;



	for (s = malloc_sizes; s->cs_size != ULONG_MAX; s++) {

		struct kmem_list3 *l3;



		l3 = s->cs_cachep->nodelists[q];

		if (!l3 || OFF_SLAB(s->cs_cachep))

			continue;



		slab_set_lock_classes(s->cs_cachep, &on_slab_l3_key,

				&on_slab_alc_key, q);

	}

}



static inline void init_lock_keys(void)
@@ -671,6 +701,14 @@ static void init_node_lock_keys(int q) 
static inline void init_lock_keys(void)

{

}



static void slab_set_debugobj_lock_classes_node(struct kmem_cache *cachep, int node)

{

}



static void slab_set_debugobj_lock_classes(struct kmem_cache *cachep)

{

}

#endif



/*
@@ -1264,6 +1302,8 @@ static int __cpuinit cpuup_prepare(long cpu) 
		spin_unlock_irq(&l3->list_lock);

		kfree(shared);

		free_alien_cache(alien);

		if (cachep->flags & SLAB_DEBUG_OBJECTS)

			slab_set_debugobj_lock_classes_node(cachep, node);

	}

	init_node_lock_keys(node);
@@ -2426,6 +2466,16 @@ kmem_cache_create (const char *name, size_t size, size_t align, 
		goto oops;

	}



	if (flags & SLAB_DEBUG_OBJECTS) {

		/*

		 * Would deadlock through slab_destroy()->call_rcu()->

		 * debug_object_activate()->kmem_cache_alloc().

		 */

		WARN_ON_ONCE(flags & SLAB_DESTROY_BY_RCU);



		slab_set_debugobj_lock_classes(cachep);

	}



	/* cache setup completed, link it into the list */

	list_add(&cachep->next, &cache_chain);

oops:

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