Le mardi 17 janvier 2012 à 09:12 -0600, Christoph Lameter a écrit :
> On Sun, 15 Jan 2012, Eric Dumazet wrote:
>
> > As soon as the slub_lock is released, another thread can come and find
> > the new kmem_cache.
>
> Slabs are not looked up by name. A pointer to kmem_cache is passed to slab
> functions and that pointer is returned from kmem_cache_create(). The risk
> is someone traversing the kmem_cach list which is only done from within slub.
>
>
> Subject: slub: Do not hold slub_lock when calling sysfs_slab_add()
>
> sysfs_slab_add() calls various sysfs functions that actually may
> end up in userspace doing all sorts of things.
>
> Release the slub_lock after adding the kmem_cache structure to the list.
> At that point the address of the kmem_cache is not known so we are
> guaranteed exlusive access to the following modifications to the
> kmem_cache structure.
>
> If the sysfs_slab_add fails then reacquire the slub_lock to
> remove the kmem_cache structure from the list.
>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> ---
> mm/slub.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/mm/slub.c
> ===================================================================
> --- linux-2.6.orig/mm/slub.c 2012-01-17 03:07:11.140010438 -0600
> +++ linux-2.6/mm/slub.c 2012-01-17 03:07:19.532010264 -0600
> @@ -3929,13 +3929,15 @@ struct kmem_cache *kmem_cache_create(con
> 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);
> + up_write(&slub_lock);
> kfree(n);
> kfree(s);
> goto err;
> }
> - up_write(&slub_lock);
> return s;
> }
> kfree(n);
Buggy patch, since "goto err;" is going to up_write(&slub_lock) again.
Also Christoph, you forgot to add the very much needed :
Reported-by: Sasha Levin <levinsasha928@xxxxxxxxx>
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