From: Tejun Heo <tj@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Zhang Qiao <zhangqiao22@huawei.com>,
mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kernel/sched: Fix sched_fork() access an invalid sched_task_group
Date: Mon, 30 Aug 2021 07:32:07 -1000 [thread overview]
Message-ID: <YS0WF0sxr0ysb6Za@mtj.duckdns.org> (raw)
In-Reply-To: <YSztujInfNNXkG5/@hirez.programming.kicks-ass.net>
Hello,
On Mon, Aug 30, 2021 at 04:39:54PM +0200, Peter Zijlstra wrote:
> > When a new process is forked, cgroup_post_fork() associates it
> > with the cgroup of its parent. Therefore this commit move the
> > __set_task_cpu() and task_fork() that access some cgroup-related
> > fields(sched_task_group and cfs_rq) to sched_post_fork() and
> > call sched_post_fork() after cgroup_post_fork().
I think this would allow cgroup migrations to take place before
sched_post_fork() is run, which likely will break stuff. The right
thing to do likely is taking sched_task_group (and whatever other
fields) after cgroup_can_fork(), which fixates the cgroup memberships,
is run. For other controllers, operations like this would be performed
from cgroup_subsys->fork() callback but it's tricky for sched due to
autogroup.
> > Fixes: 8323f26ce342 ("sched: Fix race in task_group")
> > Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com>
>
> Hmm, I think you're right. Did something recently chagne in cgroup land
> to make this more visible? This code hasn't changed in like 9 years.
I can't think of any remotely recent change either. I guess ppl just
don't try to migrate the parent while fork is in progress.
Thanks.
--
tejun
next prev parent reply other threads:[~2021-08-30 17:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-26 11:26 [PATCH] kernel/sched: Fix sched_fork() access an invalid sched_task_group Zhang Qiao
2021-08-30 11:49 ` Zhang Qiao
2021-08-30 14:39 ` Peter Zijlstra
2021-08-30 17:32 ` Tejun Heo [this message]
2021-08-31 7:58 ` Zhang Qiao
2021-08-31 22:59 ` Tejun Heo
2021-09-01 7:43 ` Zhang Qiao
2021-09-01 16:45 ` Tejun Heo
2021-09-02 7:42 ` Zhang Qiao
2021-09-07 17:01 ` Tejun Heo
2021-09-08 11:32 ` Zhang Qiao
2021-09-08 16:29 ` Tejun Heo
2021-09-09 9:45 ` Zhang Qiao
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