Messages in this thread | | | Subject | Re: [PATCH] kernel/sched: Fix sched_fork() access an invalid sched_task_group | From | Zhang Qiao <> | Date | Tue, 31 Aug 2021 15:58:42 +0800 |
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hi, thanks for your reviews.
On 2021/8/31 1:32, Tejun Heo wrote: > 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, But it still seems possible that it accessed an invalid sched_task_group? because the child process does not update its sched_task_group util cgroup_post_fork(). > 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 think this problem has always existed. I've reproduced it in multiple versions, including 3.10 and 5.14-rc3.
> > 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. >
thandks.
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