Re: [PATCH] cgroup: namespace: replace BUG_ON() in copy_cgroup_ns() with WARN_ON_ONCE()

[Michal Koutný]

Hi Shaojie.


On Wed, Sep 02, 2026 at 06:18:56PM +0800, Shaojie Sun <sunshaojie@xxxxxxxxxx> wrote:
> copy_cgroup_ns() uses BUG_ON() to guard against a NULL old_ns. The
> condition cannot currently be triggered by any caller, and the sole
> caller, create_new_namespaces(), already checks the return value with
> IS_ERR() and unwinds correctly.
> 
> Replace the BUG_ON() with WARN_ON_ONCE() and return -EINVAL instead,
> consistent with the policy of not killing the whole machine for a
> recoverable programming error.

Do you plan to tackle other namespaces too? (Adding their guys to Cc:)

It'd be good to have some consistency across them if this is going to be
touched. (I see that some simply don't care whereas others have the same
BUG_ON(). I might personally prefer the former)

Regards,
Michal


> 
> Signed-off-by: Shaojie Sun <sunshaojie@xxxxxxxxxx>
> ---
>  kernel/cgroup/namespace.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/namespace.c b/kernel/cgroup/namespace.c
> index ea4ee13936be..13930955c254 100644
> --- a/kernel/cgroup/namespace.c
> +++ b/kernel/cgroup/namespace.c
> @@ -53,7 +53,8 @@ struct cgroup_namespace *copy_cgroup_ns(u64 flags,
>  	struct ucounts *ucounts;
>  	struct css_set *cset;
>  
> -	BUG_ON(!old_ns);
> +	if (WARN_ON_ONCE(!old_ns))
> +		return ERR_PTR(-EINVAL);
>  
>  	if (!(flags & CLONE_NEWCGROUP)) {
>  		get_cgroup_ns(old_ns);
> -- 
> 2.50.1
>

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