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SubjectRe: slab: clean up kmem_cache_create_memcg() error handling
On Fri, Jan 24, 2014 at 03:33:41AM +0000, Linux Kernel wrote:
> Gitweb: http://git.kernel.org/linus/;a=commit;h=3965fc3652244651006ebb31c8c45318ce84818f
> Commit: 3965fc3652244651006ebb31c8c45318ce84818f
> Parent: 309381feaee564281c3d9e90fbca8963bb7428ad
> Author: Vladimir Davydov <vdavydov@parallels.com>
> AuthorDate: Thu Jan 23 15:52:55 2014 -0800
> Committer: Linus Torvalds <torvalds@linux-foundation.org>
> CommitDate: Thu Jan 23 16:36:50 2014 -0800
>
> slab: clean up kmem_cache_create_memcg() error handling
>
> Currently kmem_cache_create_memcg() backoffs on failure inside
> conditionals, without using gotos. This results in the rollback code
> duplication, which makes the function look cumbersome even though on
> error we should only free the allocated cache. Since in the next patch
> I am going to add yet another rollback function call on error path
> there, let's employ labels instead of conditionals for undoing any
> changes on failure to keep things clean.

...

> +out_unlock:
> mutex_unlock(&slab_mutex);
> put_online_cpus();
>
> if (err) {
> -
> if (flags & SLAB_PANIC)
> panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
> name, err);
> @@ -236,11 +230,14 @@ out_locked:
> name, err);
> dump_stack();
> }
> -
> return NULL;
> }
> -
> return s;
> +
> +out_free_cache:
> + kfree(s->name);
> + kmem_cache_free(kmem_cache, s);
> + goto out_unlock;
> }
This is now returning a freed pointer as 's' if an error occurs.
Perhaps the patch below ?

Dave


diff --git a/mm/slab_common.c b/mm/slab_common.c
index 8e40321da091..2c62294cee23 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -257,6 +257,7 @@ out_free_cache:
memcg_free_cache_params(s);
kfree(s->name);
kmem_cache_free(kmem_cache, s);
+ s = NULL;
goto out_unlock;
}


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