On Mon, Aug 20, 2012 at 08:59:37AM +0800, Li Zefan wrote: > 于 2012/8/18 2:28, Neil Horman 写道: > > On Fri, Aug 17, 2012 at 04:58:12PM +0200, Daniel Wagner wrote: > >> From: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx> > >> > >> The module version of task_cls_classid() checks if net_cls_sbusys_id > >> is valid to indentify when it is okay to access the controller. > >> > >> Instead relying on the subusys_id to be set, make it explicit > >> with a jump label. > >> > >> Signed-off-by: Daniel Wagner <daniel.wagner@xxxxxxxxxxxx> > >> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > >> Cc: Gao feng <gaofeng@xxxxxxxxxxxxxx> > >> Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx> > >> Cc: John Fastabend <john.r.fastabend@xxxxxxxxx> > >> Cc: Li Zefan <lizefan@xxxxxxxxxx> > >> Cc: Neil Horman <nhorman@xxxxxxxxxxxxx> > >> Cc: Tejun Heo <tj@xxxxxxxxxx> > >> Cc: netdev@xxxxxxxxxxxxxxx > >> Cc: cgroups@xxxxxxxxxxxxxxx > >> --- > >> include/net/cls_cgroup.h | 5 ++++- > >> net/core/sock.c | 5 +++++ > >> net/sched/cls_cgroup.c | 9 +++++++++ > >> 3 files changed, 18 insertions(+), 1 deletion(-) > >> > >> diff --git a/include/net/cls_cgroup.h b/include/net/cls_cgroup.h > >> index 401672c..bbbd957 100644 > >> --- a/include/net/cls_cgroup.h > >> +++ b/include/net/cls_cgroup.h > >> @@ -16,6 +16,7 @@ > >> #include <linux/cgroup.h> > >> #include <linux/hardirq.h> > >> #include <linux/rcupdate.h> > >> +#include <linux/jump_label.h> > >> > >> #ifdef CONFIG_CGROUPS > >> struct cgroup_cls_state > >> @@ -44,6 +45,8 @@ static inline u32 task_cls_classid(struct task_struct *p) > >> } > >> > >> #elif IS_MODULE(CONFIG_NET_CLS_CGROUP) > >> +extern struct static_key cgroup_cls_enabled; > >> +#define clscg_enabled static_key_false(&cgroup_cls_enabled) > >> > >> extern int net_cls_subsys_id; > >> > >> @@ -52,7 +55,7 @@ static inline u32 task_cls_classid(struct task_struct *p) > >> int id; > >> u32 classid = 0; > >> > >> - if (in_interrupt()) > >> + if (!clscg_enabled || in_interrupt()) > >> return 0; > >> > >> rcu_read_lock(); > >> diff --git a/net/core/sock.c b/net/core/sock.c > >> index 8f67ced..8106e77 100644 > >> --- a/net/core/sock.c > >> +++ b/net/core/sock.c > >> @@ -327,6 +327,11 @@ int __sk_backlog_rcv(struct sock *sk, struct sk_buff *skb) > >> EXPORT_SYMBOL(__sk_backlog_rcv); > >> > >> #if defined(CONFIG_CGROUPS) > >> +#if IS_MODULE(CONFIG_NET_CLS_CGROUP) > >> +struct static_key cgroup_cls_enabled = STATIC_KEY_INIT_FALSE; > >> +EXPORT_SYMBOL_GPL(cgroup_cls_enabled); > >> +#endif > >> + > >> #if !defined(CONFIG_NET_CLS_CGROUP) > >> int net_cls_subsys_id = -1; > >> EXPORT_SYMBOL_GPL(net_cls_subsys_id); > >> diff --git a/net/sched/cls_cgroup.c b/net/sched/cls_cgroup.c > >> index 7743ea8..0635894 100644 > >> --- a/net/sched/cls_cgroup.c > >> +++ b/net/sched/cls_cgroup.c > >> @@ -44,12 +44,21 @@ static struct cgroup_subsys_state *cgrp_create(struct cgroup *cgrp) > >> > >> if (cgrp->parent) > >> cs->classid = cgrp_cls_state(cgrp->parent)->classid; > >> +#if IS_MODULE(CONFIG_NET_CLS_CGROUP) > >> + else if (!clscg_enabled) > >> + static_key_slow_inc(&cgroup_cls_enabled); > > This is racy I think. The read of the static key is atomic with other reads, > > but the entire conditional is not atomic. If two cpus were creating cgroups in > > parallel, it would be possible for both to read the static key as being zero > > (the second cpu would read the key before the first cpu could increment it). > > static_key_slow_inc() is called only when we're creating the root cgroup, and that's > module loading. > > so it's safe. > What makes you say that? It appears to me that we call ss->create (and potential ss->destroy, depending on failure conditions) from cgroup_create, which in turn is called from cgroup_mkdir, which is called for every cgroup instance created, not just the root cgroup. Neil -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
