linux-kernel - Re: [PATCH] sched: fix another race when reading /proc/sched

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Date:	Fri, 12 Dec 2008 17:08:02 +0530
From:	"Bharata B Rao" <bharata.rao@...il.com>
To:	"Li Zefan" <lizf@...fujitsu.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Paul Menage" <menage@...gle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: fix another race when reading /proc/sched_debug

On Fri, Dec 12, 2008 at 3:23 PM, Li Zefan <lizf@...fujitsu.com> wrote:
>  kernel/sched_debug.c |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
> index 26ed8e3..01abf5b 100644
> --- a/kernel/sched_debug.c
> +++ b/kernel/sched_debug.c
> @@ -127,8 +127,11 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
>        if (tg)
>                cgroup = tg->css.cgroup;
>
> -       if (cgroup)
> +       if (cgroup) {
> +               cgroup_lock();
>                cgroup_path(cgroup, path, sizeof(path));
> +               cgroup_unlock();
> +       }
>
>        SEQ_printf(m, "\ncfs_rq[%d]:%s\n", cpu, path);
>  #else
> @@ -181,8 +184,11 @@ void print_rt_rq(struct seq_file *m, int cpu, struct rt_rq *rt_rq)
>        if (tg)
>                cgroup = tg->css.cgroup;
>
> -       if (cgroup)
> +       if (cgroup) {
> +               cgroup_lock();
>                cgroup_path(cgroup, path, sizeof(path));
> +               cgroup_unlock();
> +       }
>
>        SEQ_printf(m, "\nrt_rq[%d]:%s\n", cpu, path);
>  #else

The comment in cgroup_path() routine says that it needs to be called
with cgroup_mutex held. With the above fix, print_task() in
sched_debug.c remains the last caller of cgroup_path() which calls it
without holding cgroup_mutex. Does this also need a fix ?

Regards,
Bharata.
-- 
http://bharata.sulekha.com/blog/posts.htm
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