Messages in this thread | | | Date | Mon, 30 Aug 2021 07:32:07 -1000 | From | Tejun Heo <> | Subject | Re: [PATCH] kernel/sched: Fix sched_fork() access an invalid sched_task_group |
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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
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