Re: Hung task when calling clone() due to netfilter/slab

[Christoph Lameter <cl@xxxxxxxxx>]

On Tue, 17 Jan 2012, Eric Dumazet wrote:

> 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>


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.

Reported-by: Sasha Levin <levinsasha928@xxxxxxxxx>
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>

---
 mm/slub.c |    3 ++-
 1 file changed, 2 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 03:26:06.799986908 -0600
@@ -3929,13 +3929,14 @@ 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);
 				kfree(n);
 				kfree(s);
 				goto err;
 			}
-			up_write(&slub_lock);
 			return s;
 		}
 		kfree(n);
--
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