linux-kernel - Re: [PATCH] kernel/sched: fix KMSAN uninit-value error

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Date:   Mon, 5 Sep 2022 11:14:27 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Bernard Zhao <bernard@...o.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, zhaojunkui2008@....com
Subject: Re: [PATCH] kernel/sched: fix KMSAN uninit-value error

On Sun,  4 Sep 2022 19:37:14 -0700
Bernard Zhao <bernard@...o.com> wrote:

> syzbot link:
> https://syzkaller.appspot.com/bug?id=d04c5407207d11e46007775517b97764174bc45d
> 
> Signed-off-by: Bernard Zhao <bernard@...o.com>
> ---
>  kernel/sched/psi.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index ecb4b4ff4ce0..46f048121520 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -195,6 +195,9 @@ static void group_init(struct psi_group *group)
>  	init_waitqueue_head(&group->poll_wait);
>  	timer_setup(&group->poll_timer, poll_timer_fn, 0);
>  	rcu_assign_pointer(group->poll_task, NULL);
> +	memset(group->avg_total, 0, sizeof(group->avg_total));
> +	memset(group->total, 0, sizeof(group->total));
> +	memset(group->avg, 0, sizeof(group->avg));
>  }

group_init() is only called in two places. One for a static variable which
will already have all the non-set fields initialized to zero. The other can
have kmalloc() converted to kzalloc() and not worry about zeroing any of
the fields in initialization.

-- Steve

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index ec66b40bdd40..00d62681ea6a 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -957,7 +957,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
 	if (static_branch_likely(&psi_disabled))
 		return 0;
 
-	cgroup->psi = kmalloc(sizeof(struct psi_group), GFP_KERNEL);
+	cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL);
 	if (!cgroup->psi)
 		return -ENOMEM;