| Message ID | 20140516170959.GG5379@htj.dyndns.org |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 05/16/2014 11:09 AM, Tejun Heo wrote: > 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. During early init, > cgrp_dfl_root self css refcnt is used. 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 for root cgroups of non-dfl hierarchies 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 and cgroup_dfl_root self css. > > v2: cgrp_dfl_root.self is the offending one. Set the flag on it. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Reported-by: Stephen Warren <swarren@wwwdotorg.org> > Fixes: 9395a4500404 ("cgroup: enable refcnting for root csses") > --- > Hello, > > Can you try this one instead? Yes, this one works great, thanks. Tested-by: Stephen Warren <swarren@nvidia.com> -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, May 16, 2014 at 11:19:24AM -0600, Stephen Warren wrote: > On 05/16/2014 11:09 AM, Tejun Heo wrote: > > Can you try this one instead? > > Yes, this one works great, thanks. > Tested-by: Stephen Warren <swarren@nvidia.com> Thanks, I reverted the original one and applied the updated one w/ your Tested-by tag added.
--- 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 */ 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(str */ 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 */ --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4593,11 +4593,17 @@ static void __init cgroup_init_subsys(st /* 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); } @@ -4636,6 +4642,8 @@ int __init cgroup_init_early(void) int i; init_cgroup_root(&cgrp_dfl_root, &opts); + cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF; + RCU_INIT_POINTER(init_task.cgroups, &init_css_set); for_each_subsys(ss, i) { @@ -4684,7 +4692,6 @@ 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);
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. During early init, cgrp_dfl_root self css refcnt is used. 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 for root cgroups of non-dfl hierarchies 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 and cgroup_dfl_root self css. v2: cgrp_dfl_root.self is the offending one. Set the flag on it. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Stephen Warren <swarren@wwwdotorg.org> Fixes: 9395a4500404 ("cgroup: enable refcnting for root csses") --- Hello, Can you try this one instead? Thanks. include/linux/cgroup.h | 11 ++++++++--- kernel/cgroup.c | 11 +++++++++-- 2 files changed, 17 insertions(+), 5 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html