Re: [PATH v2] cgroup: add cgroup_favordynmods= command-line option

[Waiman Long <longman@xxxxxxxxxx>]

On 9/6/23 02:58, Kamalesh Babulal wrote:
> On 9/6/23 06:27, Luiz Capitulino wrote:
> [...]
> > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> > index 1fb7f562289d..2b7d74304606 100644
> > --- a/kernel/cgroup/cgroup.c
> > +++ b/kernel/cgroup/cgroup.c
> > @@ -207,6 +207,8 @@ static u16 have_exit_callback __read_mostly;
> >   static u16 have_release_callback __read_mostly;
> >   static u16 have_canfork_callback __read_mostly;
> >   
> > +static bool have_favordynmods __ro_after_init = IS_ENABLED(CONFIG_CGROUP_FAVOR_DYNMODS);
> > +
> >   /* cgroup namespace for init task */
> >   struct cgroup_namespace init_cgroup_ns = {
> >   	.ns.count	= REFCOUNT_INIT(2),
> > @@ -2243,9 +2245,9 @@ static int cgroup_init_fs_context(struct fs_context *fc)
> >   	fc->user_ns = get_user_ns(ctx->ns->user_ns);
> >   	fc->global = true;
> >   
> > -#ifdef CONFIG_CGROUP_FAVOR_DYNMODS
> > -	ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
> > -#endif
> > +	if (have_favordynmods)
> > +		ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
> > +
> >   	return 0;
> >   }
> >   
> > @@ -6764,6 +6766,12 @@ static int __init enable_cgroup_debug(char *str)
> >   }
> >   __setup("cgroup_debug", enable_cgroup_debug);
> >   
> > +static int __init cgroup_favordynmods_setup(char *str)
> > +{
> > +	return (kstrtobool(str, &have_favordynmods) == 0);
> > +}
> > +__setup("cgroup_favordynmods=", cgroup_favordynmods_setup);
> > +
> >   /**
> >    * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
> >    * @dentry: directory dentry of interest
> Consider a case where the kernel is compiled with
> CONFIG_CGROUP_FAVOR_DYNMODS=n and kernel command line is passed with
> cgroup_favordynmods=true, this would set the have_favordynmods to true.
> In cgroup_favordynmods_setup(), should it return 0 with a pr_warn(),
> when CONFIG_CGROUP_FAVOR_DYNMODS=n in the above case, or is this
> expected behavior?

According to the documentation of __setup:

/*
 * NOTE: __setup functions return values:
 * @fn returns 1 (or non-zero) if the option argument is "handled"
 * and returns 0 if the option argument is "not handled".
 */

So the return value should tell whether the input parameter is a 
recognizable true or false value, not whether it is true or false. 
kstrtobool returns 0 if it is a recognizable T/F value or -EINVAL 
otherwise. So the check is correct. I did double check that before I 
ack'ed the patch.

Cheers,
Longman