| Message ID | 20140516154330.GB5379@htj.dyndns.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 05/16/2014 09:43 AM, Tejun Heo wrote: > From 49035d695d8f1c4bbe4e37480e5d06812818947c Mon Sep 17 00:00:00 2001 > From: Tejun Heo <tj@kernel.org> > Date: Fri, 16 May 2014 11:40:33 -0400 > > 9395a4500404 ("cgroup: enable refcnting for root csses") enabled > reference counting for root csses (cgroup_subsys_states) so that > cgroup's self csses can be used to manage the lifetime of the > containing cgroups. > > Unfortunately, this change was incorrect. cpu controller uses > early_init and starts using css reference counts on its root css from > then on. percpu_ref can't initialized during early init and its > initialization is deferred till cgroup_init() time. This means that > cpu was using percpu_ref which wasn't properly initialized. Due to > the way percpu variables are laid out on x86, this didn't blow up > immediately on x86 but ended up incrementing and decrementing the > percpu variable at offset zero, whatever it may be; however, on other > archs, this caused fault and early boot failure. > > As cgroup self csses still need working refcounting, we can't revert > 9395a4500404. This patch adds CSS_NO_REF which explicitly inhibits > reference counting on the css and sets it on all normal (non-self) > csses. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reported-by: Stephen Warren <swarren@wwwdotorg.org> > Fixes: 9395a4500404 ("cgroup: enable refcnting for root csses") > --- > Patch applied to cgroup/for-3.16. Unfortunately, this patch doesn't seem to solve the problem for me. I still get a hang/crash very early during boot, before earlyprintk stars. I tried this patch on top of both next-20150115, and next-20150516. For both those kernels, reverting the original problematic patch does resolve the problem. I'll try to investigate more later today.
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 76dadd77..1737db0 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -77,6 +77,7 @@ struct cgroup_subsys_state { /* bits in struct cgroup_subsys_state flags field */ enum { + CSS_NO_REF = (1 << 0), /* no reference counting for this css */ CSS_ONLINE = (1 << 1), /* between ->css_online() and ->css_offline() */ }; @@ -88,7 +89,8 @@ enum { */ static inline void css_get(struct cgroup_subsys_state *css) { - percpu_ref_get(&css->refcnt); + if (!(css->flags & CSS_NO_REF)) + percpu_ref_get(&css->refcnt); } /** @@ -103,7 +105,9 @@ static inline void css_get(struct cgroup_subsys_state *css) */ static inline bool css_tryget_online(struct cgroup_subsys_state *css) { - return percpu_ref_tryget_live(&css->refcnt); + if (!(css->flags & CSS_NO_REF)) + return percpu_ref_tryget_live(&css->refcnt); + return true; } /** @@ -114,7 +118,8 @@ static inline bool css_tryget_online(struct cgroup_subsys_state *css) */ static inline void css_put(struct cgroup_subsys_state *css) { - percpu_ref_put(&css->refcnt); + if (!(css->flags & CSS_NO_REF)) + percpu_ref_put(&css->refcnt); } /* bits in struct cgroup flags field */ diff --git a/kernel/cgroup.c b/kernel/cgroup.c index c01e8e8..ad15bb7 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4593,11 +4593,17 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early) /* We don't handle early failures gracefully */ BUG_ON(IS_ERR(css)); init_and_link_css(css, ss, &cgrp_dfl_root.cgrp); + + /* + * Root csses are never destroyed and we can't initialize + * percpu_ref during early init. Disable refcnting. + */ + css->flags |= CSS_NO_REF; + if (early) { /* allocation can't be done safely during early init */ css->id = 1; } else { - BUG_ON(percpu_ref_init(&css->refcnt, css_release)); css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL); BUG_ON(css->id < 0); } @@ -4684,7 +4690,6 @@ int __init cgroup_init(void) struct cgroup_subsys_state *css = init_css_set.subsys[ss->id]; - BUG_ON(percpu_ref_init(&css->refcnt, css_release)); css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL); BUG_ON(css->id < 0);