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SubjectRe: [PATCH SLAB 1/2 v3] duplicate the cache name in SLUB's saved_alias list, SLAB, and SLOB
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On Fri, 2012-07-06 at 08:56 -0500, Christoph Lameter wrote:
> I thought I posted this a couple of days ago. Would this not fix things
> without having to change all the allocators?

I was pointed by Glauber to the slab common code patches. I need some
more time to read the patches. Now I think the slab/slot changes in this
v3 are not needed, and can be ignored.

But for the SLUB's saved_alias list issue, I don't think the following
patch helps. Details below: (Maybe I am wrong, as I'm reading the patch
based on the 3.5-rc6 code ...)

>
>
> Subject: slub: Dup name earlier in kmem_cache_create
>
> Dup the name earlier in kmem_cache_create so that alias
> processing is done using the copy of the string and not
> the string itself.
>
> Signed-off-by: Christoph Lameter <cl@linux.com>
>
> ---
> mm/slub.c | 29 ++++++++++++++---------------
> 1 file changed, 14 insertions(+), 15 deletions(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2012-06-11 08:49:56.000000000 -0500
> +++ linux-2.6/mm/slub.c 2012-07-03 15:17:37.000000000 -0500
> @@ -3933,8 +3933,12 @@ struct kmem_cache *kmem_cache_create(con
> if (WARN_ON(!name))
> return NULL;
>
> + n = kstrdup(name, GFP_KERNEL);
> + if (!n)
> + goto out;
> +
> down_write(&slub_lock);
> - s = find_mergeable(size, align, flags, name, ctor);
> + s = find_mergeable(size, align, flags, n, ctor);
> if (s) {
> s->refcount++;
> /*

......
up_write(&slub_lock);
return s;
}
Here, the function returns without name string n be kfreed.

But we couldn't kfree n here, because in sysfs_slab_alias(), if
(slab_state < SYS_FS), the name need to be kept valid until
slab_sysfs_init() is finished adding the entry into sysfs.

> @@ -3944,7 +3948,7 @@ struct kmem_cache *kmem_cache_create(con
> s->objsize = max(s->objsize, (int)size);
> s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
>
> - if (sysfs_slab_alias(s, name)) {
> + if (sysfs_slab_alias(s, n)) {
> s->refcount--;
> goto err;
> }
> @@ -3952,31 +3956,26 @@ struct kmem_cache *kmem_cache_create(con
> return s;
> }
>
> - n = kstrdup(name, GFP_KERNEL);
> - if (!n)
> - goto err;
> -
> s = kmalloc(kmem_size, GFP_KERNEL);
> if (s) {
> if (kmem_cache_open(s, n,
> size, align, flags, ctor)) {
> list_add(&s->list, &slab_caches);
> up_write(&slub_lock);
> - if (sysfs_slab_add(s)) {
> - down_write(&slub_lock);
> - list_del(&s->list);
> - kfree(n);
> - kfree(s);
> - goto err;
> - }
> - return s;
> + if (!sysfs_slab_add(s))
> + return s;
> +
> + down_write(&slub_lock);
> + list_del(&s->list);
> }
> kfree(s);
> }
> - kfree(n);
> +
> err:
> + kfree(n);
> up_write(&slub_lock);
>
> +out:
> if (flags & SLAB_PANIC)
> panic("Cannot create slabcache %s\n", name);
> else
>




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