[Devel] Re: [PATCH 1/2] cgroups: Fix to return errno in a failure path

[Serge E. Hallyn]

Quoting Li Zefan (lizf at cn.fujitsu.com):
> In cgroup_create(), if alloc_css_id() returns failure, the errno
> is not propagated to userspace, so mkdir will fail silently.
> 
> To trigger this bug, we mount blkio (or memory subsystem), and
> create more then 65534 cgroups. (The number of cgroups is limited
> to 65535 if a subsystem has use_id == 1)
> 
>  # mount -t cgroup -o blkio xxx /mnt
>  # for ((i = 0; i < 65534; i++)); do mkdir /mnt/$i; done
>  # mkdir /mnt/65534
>  (should return ENOSPC)
>  #
> 
> Signed-off-by: Li Zefan <lizf at cn.fujitsu.com>

Yup.

Acked-by: Serge Hallyn <serue at us.ibm.com>

> ---
>  cgroup.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> --- a/kernel/cgroup.c.orig	2010-01-19 16:37:37.000000000 +0800
> +++ a/kernel/cgroup.c	2010-01-19 16:39:07.000000000 +0800
> @@ -3279,14 +3279,17 @@ static long cgroup_create(struct cgroup 
> 
>  	for_each_subsys(root, ss) {
>  		struct cgroup_subsys_state *css = ss->create(ss, cgrp);
> +
>  		if (IS_ERR(css)) {
>  			err = PTR_ERR(css);
>  			goto err_destroy;
>  		}
>  		init_cgroup_css(css, ss, cgrp);
> -		if (ss->use_id)
> -			if (alloc_css_id(ss, parent, cgrp))
> +		if (ss->use_id) {
> +			err = alloc_css_id(ss, parent, cgrp);
> +			if (err)
>  				goto err_destroy;
> +		}
>  		/* At error, ->destroy() callback has to free assigned ID. */
>  	}
> 
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