linux-kernel - Re: [PATCH] cgroups: fix probable race with put_css_set[_taskexit] and find_css

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Message-ID: <6599ad830809092011x6fce5a70kcd4fb77bf37c46a2@mail.gmail.com>
Date:	Tue, 9 Sep 2008 20:11:39 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Lai Jiangshan" <laijs@...fujitsu.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Greg Kroah-Hartman" <greg@...ah.com>
Subject: Re: [PATCH] cgroups: fix probable race with put_css_set[_taskexit] and find_css_set

On Tue, Sep 9, 2008 at 7:18 PM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
>        hlist_for_each_entry(cg, node, hhead, hlist) {
>                if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
>                        /* All subsystems matched */
> +                       if (!kref_get_not_zero(&cg->ref))
> +                               return NULL;

Maybe it would be better to do:

if (!memcmp(...) && kref_get_not_zero(&cg->ref))
  return cg;

so that in the event of a race, we carry on looking in the array.
> + * Return 0 if this refcount is 0, otherwise return 1.
> + */
> +int kref_get_not_zero(struct kref *kref)

Probably clearer to have a bool return type.

Paul
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