On 10/29/2012 06:49 PM, Glauber Costa wrote:
> 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.
Hi, Glauber
I'm trying to understand what's the issue we are trying to solve, but
looks like I need some help...
So allow me to ask few questions:
1. what's scene will cause the fake dead lock?
2. what's the conflict caches?
3. how does their lock operation nested?
And I think it will be better if we have the bug log in patch comment,
so folks will easily know what's the reason we need this patch ;-)
Regards,
Michael Wang
>
> Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
> CC: Christoph Lameter <cl@xxxxxxxxx>
> CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> CC: David Rientjes <rientjes@xxxxxxxxxx>
> CC: JoonSoo Kim <js1304@xxxxxxxxx>
>
> ---
> 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;
> }
>
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>