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SubjectRe: [PATCH V2] mm/slab: add a leak decoder callback
Hello, Liu Bo.

On Wed, Jan 16, 2013 at 11:03:13AM +0800, Liu Bo wrote:
> This adds a leak decoder callback so that slab destruction
> can use to generate debugging output for the allocated objects.
>
> Callers like btrfs are using their own leak tracking which will
> manage allocated objects in a list(or something else), this does
> indeed the same thing as what slab does. So adding a callback
> for leak tracking can avoid this as well as runtime overhead.
>
> (The idea is from Zach Brown <zab@zabbo.net>.)
>
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> ---
> v2: add a wrapper API for slab destruction to make decoder only
> work in particular path.
>
> fs/btrfs/extent_io.c | 26 ++++++++++++++++++++++++--
> fs/btrfs/extent_map.c | 13 ++++++++++++-
> include/linux/slab.h | 2 ++
> include/linux/slab_def.h | 1 +
> include/linux/slub_def.h | 1 +
> mm/slab_common.c | 17 ++++++++++++++++-
> mm/slub.c | 2 ++
> 7 files changed, 58 insertions(+), 4 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index bcc8dff..355c7fc 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -63,6 +63,26 @@ tree_fs_info(struct extent_io_tree *tree)
> return btrfs_sb(tree->mapping->host->i_sb);
> }
>
> +static void extent_state_leak_decoder(void *object)
> +{
> + struct extent_state *state = object;
> +
> + printk(KERN_ERR "btrfs state leak: start %llu end %llu "
> + "state %lu in tree %p refs %d\n",
> + (unsigned long long)state->start,
> + (unsigned long long)state->end,
> + state->state, state->tree, atomic_read(&state->refs));
> +}
> +
> +static void extent_buffer_leak_decoder(void *object)
> +{
> + struct extent_buffer *eb = object;
> +
> + printk(KERN_ERR "btrfs buffer leak start %llu len %lu "
> + "refs %d\n", (unsigned long long)eb->start,
> + eb->len, atomic_read(&eb->refs));
> +}
> +
> int __init extent_io_init(void)
> {
> extent_state_cache = kmem_cache_create("btrfs_extent_state",
> @@ -115,9 +135,11 @@ void extent_io_exit(void)
> */
> rcu_barrier();
> if (extent_state_cache)
> - kmem_cache_destroy(extent_state_cache);
> + kmem_cache_destroy_decoder(extent_state_cache,
> + extent_state_leak_decoder);
> if (extent_buffer_cache)
> - kmem_cache_destroy(extent_buffer_cache);
> + kmem_cache_destroy_decoder(extent_buffer_cache,
> + extent_buffer_leak_decoder);
> }
>
> void extent_io_tree_init(struct extent_io_tree *tree,
> diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
> index f359e4c..bccba3d 100644
> --- a/fs/btrfs/extent_map.c
> +++ b/fs/btrfs/extent_map.c
> @@ -16,6 +16,16 @@ static LIST_HEAD(emaps);
> static DEFINE_SPINLOCK(map_leak_lock);
> #endif
>
> +static void extent_map_leak_decoder(void *object)
> +{
> + struct extent_map *em = object;
> +
> + printk(KERN_ERR "btrfs ext map leak: start %llu len %llu block %llu "
> + "flags %lu refs %d in tree %d compress %d\n",
> + em->start, em->len, em->block_start, em->flags,
> + atomic_read(&em->refs), em->in_tree, (int)em->compress_type);
> +}
> +
> int __init extent_map_init(void)
> {
> extent_map_cache = kmem_cache_create("btrfs_extent_map",
> @@ -39,7 +49,8 @@ void extent_map_exit(void)
> }
>
> if (extent_map_cache)
> - kmem_cache_destroy(extent_map_cache);
> + kmem_cache_destroy_decoder(extent_map_cache,
> + extent_map_leak_decoder);
> }
>
> /**
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 5d168d7..5c6a8d8 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -114,6 +114,7 @@ struct kmem_cache {
> const char *name; /* Slab name for sysfs */
> int refcount; /* Use counter */
> void (*ctor)(void *); /* Called on object slot creation */
> + void (*decoder)(void *);/* Called on object slot leak detection */
> struct list_head list; /* List of all slab caches on the system */
> };
> #endif
> @@ -132,6 +133,7 @@ struct kmem_cache *
> kmem_cache_create_memcg(struct mem_cgroup *, const char *, size_t, size_t,
> unsigned long, void (*)(void *), struct kmem_cache *);
> void kmem_cache_destroy(struct kmem_cache *);
> +void kmem_cache_destroy_decoder(struct kmem_cache *, void (*)(void *));
> int kmem_cache_shrink(struct kmem_cache *);
> void kmem_cache_free(struct kmem_cache *, void *);
>

For SLUB,
kmem_cache_destroy_decoder works when CONFIG_SLUB_DEBUG is enable.
But, user for kmem_cache_destroy_decoder can't know about it.

How about below approach?

#ifdef CONFIG_SLUB_DEBUG
void kmem_cache_destroy_decoder(struct kmem_cache *, void (*)(void *));
#else
#define kmem_cache_destroy_decoder(s) kmem_cache_destory(s)
#endif

> diff --git a/include/linux/slab_def.h b/include/linux/slab_def.h
> index 8bb6e0e..7ca8309 100644
> --- a/include/linux/slab_def.h
> +++ b/include/linux/slab_def.h
> @@ -48,6 +48,7 @@ struct kmem_cache {
>
> /* constructor func */
> void (*ctor)(void *obj);
> + void (*decoder)(void *obj);
>
> /* 4) cache creation/removal */
> const char *name;
> diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
> index 9db4825..fc18af7 100644
> --- a/include/linux/slub_def.h
> +++ b/include/linux/slub_def.h
> @@ -93,6 +93,7 @@ struct kmem_cache {
> gfp_t allocflags; /* gfp flags to use on each alloc */
> int refcount; /* Refcount for slab cache destroy */
> void (*ctor)(void *);
> + void (*decoder)(void *);
> int inuse; /* Offset to metadata */
> int align; /* Alignment */
> int reserved; /* Reserved bytes at the end of slabs */
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 3f3cd97..8c19bfd 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -193,6 +193,7 @@ kmem_cache_create_memcg(struct mem_cgroup *memcg, const char *name, size_t size,
> s->object_size = s->size = size;
> s->align = calculate_alignment(flags, align, size);
> s->ctor = ctor;
> + s->decoder = NULL;
>
> if (memcg_register_cache(memcg, s, parent_cache)) {
> kmem_cache_free(kmem_cache, s);
> @@ -248,7 +249,7 @@ kmem_cache_create(const char *name, size_t size, size_t align,
> }
> EXPORT_SYMBOL(kmem_cache_create);
>
> -void kmem_cache_destroy(struct kmem_cache *s)
> +static void __kmem_cache_destroy(struct kmem_cache *s, void (*decoder)(void *))
> {
> /* Destroy all the children caches if we aren't a memcg cache */
> kmem_cache_destroy_memcg_children(s);
> @@ -259,6 +260,9 @@ void kmem_cache_destroy(struct kmem_cache *s)
> if (!s->refcount) {
> list_del(&s->list);
>
> + if (unlikely(decoder))
> + s->decoder = decoder;
> +
> if (!__kmem_cache_shutdown(s)) {
> mutex_unlock(&slab_mutex);
> if (s->flags & SLAB_DESTROY_BY_RCU)
> @@ -279,8 +283,19 @@ void kmem_cache_destroy(struct kmem_cache *s)
> }
> put_online_cpus();
> }
> +
> +void kmem_cache_destroy(struct kmem_cache *s)
> +{
> + return __kmem_cache_destroy(s, NULL);
> +}
> EXPORT_SYMBOL(kmem_cache_destroy);
>
> +void kmem_cache_destroy_decoder(struct kmem_cache *s, void (*decoder)(void *))
> +{
> + return __kmem_cache_destroy(s, decoder);
> +}
> +EXPORT_SYMBOL(kmem_cache_destroy_decoder);
> +
> int slab_is_available(void)
> {
> return slab_state >= UP;
> diff --git a/mm/slub.c b/mm/slub.c
> index ba2ca53..34b3b75 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3098,6 +3098,8 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
> for_each_object(p, s, addr, page->objects) {
>
> if (!test_bit(slab_index(p, s, addr), map)) {
> + if (unlikely(s->decoder))
> + s->decoder(p);
> printk(KERN_ERR "INFO: Object 0x%p @offset=%tu\n",
> p, p - addr);
> print_tracking(s, p);
> --
> 1.7.7.6
>
> --
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