Messages in this thread | | | From | Waiman Long <> | Subject | Re: [PATCH 1/2] cgroup: Fix incorrect warning from cgroup_apply_control_disable() | Date | Mon, 13 Sep 2021 14:35:03 -0400 |
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On 9/13/21 2:05 PM, Tejun Heo wrote: > Hello, > > On Thu, Sep 09, 2021 at 10:42:55PM -0400, Waiman Long wrote: >> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c >> index 881ce1470beb..e31bca9fcd46 100644 >> --- a/kernel/cgroup/cgroup.c >> +++ b/kernel/cgroup/cgroup.c >> @@ -3140,7 +3140,16 @@ static void cgroup_apply_control_disable(struct cgroup *cgrp) >> if (!css) >> continue; >> >> - WARN_ON_ONCE(percpu_ref_is_dying(&css->refcnt)); >> + /* >> + * A kill_css() might have been called previously, but >> + * the css may still linger for a while before being >> + * removed. Skip it in this case. >> + */ >> + if (percpu_ref_is_dying(&css->refcnt)) { >> + WARN_ON_ONCE(css->parent && >> + cgroup_ss_mask(dsct) & (1 << ss->id)); >> + continue; >> + } > This warning did help me catch some gnarly bugs. Any chance we can keep it > for normal cases and elide it just for remounting?
The problem with percpu_ref_is_dying() is the fact that it becomes true after percpu_ref_exit() is called in css_free_rwork_fn() which has an RCU delay. If you want to catch the fact that kill_css() has been called, we can check the CSS_DYING flag which is set in kill_css() by commit 33c35aa481786 ("cgroup: Prevent kill_css() from being called more than once"). Will that be an acceptable alternative?
Cheers, Longman
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