cgroup: simplify init_subsys() (v2)
PATCH 2/3 cgroup: simplify init_subsys() (v2)
Changelog v2:
-------------
1. Add a BUG_ON() to insure no processes haved been forked before all subsystems have been registered.
2. Update the document about the fork callback.
We are at system boot and there is only 1 cgroup group (i,e, init_css_set), so we don't need to run through the css_set linked list. Neither do we need to run through the task list, since no processes have been created yet.
Also referring to a comment in cgroup.h:
struct css_set
{
...
/*
* Set of subsystem states, one for each subsystem. This array
* is immutable after creation apart from the init_css_set
* during subsystem registration (at boot time).
*/
struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];
}Signed-off-by Li Zefan <[email protected]>
Reviewed-by Paul Menage <[email protected]>
---
I just resent this patch for Andrew. ;)
One of the purposes of this patch is to be a preparation for the 3rd patch. so this should be applied before that patch.
--- Documentation/cgroups.txt | 3 +-- kernel/cgroup.c | 35 +++++++++-------------------------- 2 files changed, 10 insertions(+), 28 deletions(-)
Documentation/cgroups.txt +1 -2
@@ -500,8 +500,7 @@ post-attachment activity that requires memory allocations or blocking. void fork(struct cgroup_subsy *ss, struct task_struct *task) -Called when a task is forked into a cgroup. Also called during -registration for all existing tasks. +Called when a task is forked into a cgroup. void exit(struct cgroup_subsys *ss, struct task_struct *task)
kernel/cgroup.c +9 -26
@@ -2471,7 +2471,6 @@ static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)static void __init cgroup_init_subsys (struct cgroup_subsys *ss) {struct cgroup_subsys_state *css; -struct list_head *l;printk (KERN_INFO "Initializing cgroup subsys %s\n" , ss->name);
@@ -2482,35 +2481,19 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)BUG_ON (IS_ERR (css));init_cgroup_css (css, ss, dummytop); -/* Update all cgroup groups to contain a subsys +/* Update the init_css_set to contain a subsys * pointer to this state - since the subsystem is -* newly registered, all tasks and hence all cgroup -* groups are in the subsystem's top cgroup. */ -write_lock (&css_set_lock); - l = &init_css_set.list; -do { -struct css_set *cg = - list_entry(l, struct css_set, list); - cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id]; - l = l->next; - }while (l != &init_css_set.list); -write_unlock (&css_set_lock); - -/* If this subsystem requested that it be notified with fork -* events, we should send it one now for every process in the -* system */ -if (ss->fork) { -struct task_struct *g, *p; - -read_lock (&tasklist_lock); - do_each_thread(g, p) { - ss->fork (ss, p); - }while_each_thread (g, p); -read_unlock (&tasklist_lock); - } +* newly registered, all tasks and hence the +* init_css_set is in the subsystem's top cgroup. */ + init_css_set.subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id]; need_forkexit_callback |= ss->fork || ss->exit; +/* At system boot, before all subsystems have been +* registered, no tasks have been forked, so we don't +* need to invoke fork callbacks here. */ +BUG_ON (!list_empty (&init_task.tasks)); + ss->active =1 ; }
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1.5.4.rc3