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cgroups: don't put struct cgroupfs_root protected by RCU

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We don't access struct cgroupfs_root in fast path, so we should not put
struct cgroupfs_root protected by RCU

But the comment in struct cgroup_subsys.root confuse us.

struct cgroup_subsys.root is used in these places:

1 find_css_set(): if (ss->root->subsys_list.next == &ss->sibling)
2 rebind_subsystems(): if (ss->root != &rootnode)
                       rcu_assign_pointer(ss->root, root);
                       rcu_assign_pointer(subsys[i]->root, &rootnode);
3 cgroup_has_css_refs(): if (ss->root != cgrp->root)
4 cgroup_init_subsys(): ss->root = &rootnode;
5 proc_cgroupstats_show(): ss->name, ss->root->subsys_bits,
                           ss->root->number_of_cgroups, !ss->disabled);
6 cgroup_clone(): root = subsys->root;
                  if ((root != subsys->root) ||

All these place we have held cgroup_lock() or we don't dereference to
struct cgroupfs_root.  It's means wo don't need RCU when use struct
cgroup_subsys.root, and we should not put struct cgroupfs_root protected
by RCU.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Lai Jiangshan 2009-01-07 18:07:37 -08:00 committed by Linus Torvalds
parent 2019f634ce
commit b2aa30f7bb
2 changed files with 2 additions and 3 deletions
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1
include/linux/cgroup.h
View file

@ -337,7 +337,6 @@ struct cgroup_subsys {
#define MAX_CGROUP_TYPE_NAMELEN 32 #define MAX_CGROUP_TYPE_NAMELEN 32
const char *name; const char *name;
/* Protected by RCU */
struct cgroupfs_root *root; struct cgroupfs_root *root;
struct list_head sibling; struct list_head sibling;

4
kernel/cgroup.c
View file

@ -713,7 +713,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
cgrp->subsys[i] = dummytop->subsys[i]; cgrp->subsys[i] = dummytop->subsys[i];
cgrp->subsys[i]->cgroup = cgrp; cgrp->subsys[i]->cgroup = cgrp;
list_add(&ss->sibling, &root->subsys_list); list_add(&ss->sibling, &root->subsys_list);
rcu_assign_pointer(ss->root, root); ss->root = root;
if (ss->bind) if (ss->bind)
ss->bind(ss, cgrp); ss->bind(ss, cgrp);
@ -725,7 +725,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
ss->bind(ss, dummytop); ss->bind(ss, dummytop);
dummytop->subsys[i]->cgroup = dummytop; dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL; cgrp->subsys[i] = NULL;
rcu_assign_pointer(subsys[i]->root, &rootnode); subsys[i]->root = &rootnode;
list_del(&ss->sibling); list_del(&ss->sibling);
} else if (bit & final_bits) { } else if (bit & final_bits) {
/* Subsystem state should already exist */ /* Subsystem state should already exist */