On 02/06/2014 07:21 AM, Steven Rostedt wrote:
> Vladimir reported the following issue:
>
> Commit c65c1877bd68 ("slub: use lockdep_assert_held") requires
> remove_partial() to be called with n->list_lock held, but free_partial()
> called from kmem_cache_close() on cache destruction does not follow this
> rule, leading to a warning:
>
> WARNING: CPU: 0 PID: 2787 at mm/slub.c:1536
> __kmem_cache_shutdown+0x1b2/0x1f0()
> Modules linked in:
> CPU: 0 PID: 2787 Comm: modprobe Tainted: GW3.14.0-rc1-mm1+ #1
> Hardware name:
>0600 88003ae1dde8 816d9583 0600
> 88003ae1de28 8107c107
>880037ab2b00 88007c240d30 ea0001ee5280 ea0001ee52a0
> Call Trace:
>[] dump_stack+0x51/0x6e
>[] warn_slowpath_common+0x87/0xb0
>[] warn_slowpath_null+0x15/0x20
>[] __kmem_cache_shutdown+0x1b2/0x1f0
>[] kmem_cache_destroy+0x43/0xf0
>[] xfs_destroy_zones+0x103/0x110 [xfs]
>[] exit_xfs_fs+0x38/0x4e4 [xfs]
>[] SyS_delete_module+0x19a/0x1f0
>[] ? retint_swapgs+0x13/0x1b
>[] ? trace_hardirqs_on_caller+0x105/0x1d0
>[] ? trace_hardirqs_on_thunk+0x3a/0x3f
>[] system_call_fastpath+0x16/0x1b
>
>
> His solution was to add a spinlock in order to quiet lockdep. Although
> there would be no contention to adding the lock, that lock also
> requires disabling of interrupts which will have a larger impact on the
> system.
>
> Instead of adding a spinlock to a location where it is not needed for
> lockdep, make a __remove_partial() function that does not test if
> the list_lock is held, as no one should have it due to it being freed.
>
> Also added a __add_partial() function that does not do the lock validation
> either, as it is not needed for the creation of the cache.
>
> Suggested-by: David Rientjes
> Reported-by: Vladimir Davydov
> Signed-off-by: Steven Rostedt
>
> Index: linux-trace.git/mm/slub.c
> ===
> --- linux-trace.git.orig/mm/slub.c
> +++ linux-trace.git/mm/slub.c
> @@ -1520,11 +1520,9 @@ static void discard_slab(struct kmem_cac
> /*
> * Management of partially allocated slabs.
> */
> -static inline void add_partial(struct kmem_cache_node *n,
> - struct page *page, int tail)
> +static inline void
> +__add_partial(struct kmem_cache_node *n, struct page *page, int tail)
> {
> - lockdep_assert_held(&n->list_lock);
> -
> n->nr_partial++;
> if (tail == DEACTIVATE_TO_TAIL)
> list_add_tail(&page->lru, &n->partial);
> @@ -1532,15 +1530,27 @@ static inline void add_partial(struct km
> list_add(&page->lru, &n->partial);
> }
>
> -static inline void remove_partial(struct kmem_cache_node *n,
> - struct page *page)
> +static inline void add_partial(struct kmem_cache_node *n,
> + struct page *page, int tail)
> {
> lockdep_assert_held(&n->list_lock);
> + __add_partial(n, page, tail);
> +}
>
> +static inline void
> +__remove_partial(struct kmem_cache_node *n, struct page *page)
> +{
> list_del(&page->lru);
> n->nr_partial--;
> }
>
> +static inline void remove_partial(struct kmem_cache_node *n,
> + struct page *page)
> +{
> + lockdep_assert_held(&n->list_lock);
> + __remove_partial(n, page);
> +}
> +
> /*
> * Remove slab from the partial list, freeze it and
> * return the pointer to the freelist.
> @@ -2906,12 +2916,10 @@ static void early_kmem_cache_node_alloc(
> inc_slabs_node(kmem_cache_node, node, page->objects);
>
> /*
> - * the lock is for lockdep's sake, not for any actual
> - * race protection
> + * No locks need to be taken here as it has just been
> + * initialized and there is no concurrent access.
>*/
> - spin_lock(&n->list_lock);
> - add_partial(n, page, DEACTIVATE_TO_HEAD);
> - spin_unlock(&n->list_lock);
> + __add_partial(n, page, DEACTIVATE_TO_HEAD);
> }
>
> static void free_kmem_cache_nodes(struct kmem_cache *s)
> @@ -3197,7 +3205,7 @@ static void free_partial(struct kmem_cac
>
> list_for_each_entry_safe(page, h, &n->partial, lru) {
> if (!page->inuse) {
> - remove_partial(n, page);
> + __remove_partial(n, page);
> discard_slab(s, page);
> } else {
> list_slab_objects(s, page,
Looks neat.
FWIW,
Acked-by: Vladimir Davydov
Thanks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
