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    SubjectRe: [patch] lockdep: annotate mm/slab.c

    * Linus Torvalds <torvalds@osdl.org> wrote:

    > Why isn't the "on_slab_key" local to just the init_lock_keys()
    > function, and the #ifdef around it all?

    yeah - find updated patch below.

    Ingo

    ------->
    Subject: lockdep: annotate mm/slab.c
    From: Arjan van de Ven <arjan@infradead.org>

    mm/slab.c uses nested locking when dealing with 'off-slab'
    caches, in that case it allocates the slab header from the
    (on-slab) kmalloc caches. Teach the lock validator about
    this by putting all on-slab caches into a separate class.

    this patch has no effect on non-lockdep kernels.

    Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    mm/slab.c | 25 +++++++++++++++++++++++++
    1 file changed, 25 insertions(+)

    Index: linux/mm/slab.c
    ===================================================================
    --- linux.orig/mm/slab.c
    +++ linux/mm/slab.c
    @@ -674,6 +674,30 @@ static struct kmem_cache cache_cache = {
    #endif
    };

    +/*
    + * Slab sometimes uses the kmalloc slabs to store the slab headers
    + * for other slabs "off slab".
    + * The locking for this is tricky in that it nests within the locks
    + * of all other slabs in a few places; to deal with this special
    + * locking we put on-slab caches into a separate lock-class.
    + */
    +static inline void init_lock_keys(struct cache_sizes *s)
    +{
    +#ifdef CONFIG_LOCKDEP
    + static struct lock_class_key on_slab_key;
    + int q;
    +
    + for (q = 0; q < MAX_NUMNODES; q++) {
    + if (!s->cs_cachep->nodelists[q] || OFF_SLAB(s->cs_cachep))
    + continue;
    + lockdep_set_class(&s->cs_cachep->nodelists[q]->list_lock,
    + &on_slab_key);
    + }
    +#endif
    +}
    +
    +
    +
    /* Guard access to the cache-chain. */
    static DEFINE_MUTEX(cache_chain_mutex);
    static struct list_head cache_chain;
    @@ -1391,6 +1415,7 @@ void __init kmem_cache_init(void)
    ARCH_KMALLOC_FLAGS|SLAB_PANIC,
    NULL, NULL);
    }
    + init_lock_keys(sizes);

    sizes->cs_dmacachep = kmem_cache_create(names->name_dma,
    sizes->cs_size,
    -
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