Messages in this thread | | | Date | Wed, 1 Jun 2022 17:40:51 -0700 | From | Tadeusz Struk <> | Subject | Re: [PATCH 2/2] cgroup: Use separate work structs on css release path |
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On 6/1/22 17:29, Tejun Heo wrote: > On Wed, Jun 01, 2022 at 05:26:34PM -0700, Tadeusz Struk wrote: >> Ok the problem is that >> >> 1. kill_css() triggers css_killed_ref_fn(), which enqueues &css->destroy_work on cgroup_destroy_wq >> 2. Last put_css() calls css_release(), which enqueues &css->destroy_work on cgroup_destroy_wq >> >> We have two instances of the same work struct enqueued on the same WQ (cgroup_destroy_wq), >> which causes "BUG: corrupted list in insert_work" > > #2 shouldn't be happening before kill_ref_fn() is done with the css. If what > you're saying is happening, what's broken is the fact that the refcnt is > reaching 0 prematurely.
css_killed_ref_fn() will be called regardless of the value of refcnt (via percpu_ref_kill_and_confirm()) and it will only enqueue the css_killed_work_fn() to be called later. Then css_put()->css_release() will be called before the css_killed_work_fn() will even get a chance to run, and it will also *only* enqueue css_release_work_fn() to be called later. The problem happens on the second enqueue. So there need to be something in place that will make sure that css_killed_work_fn() is done before css_release() can enqueue the second job. Does it sound right?
>> So I think the easiest way to solve this would be to have two separate work_structs, >> one for the killed_ref path and css_release path as in: > > If you do that, you'd just be racing the free path against the kill path and > the css might get freed while the kill path is still accessing it. > > Thanks. >
-- Thanks, Tadeusz
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