The patch titled
cgroups: don't put struct cgroupfs_root protected by RCU
has been added to the -mm tree. Its filename is
cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu.patch
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Subject: cgroups: don't put struct cgroupfs_root protected by RCU
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Reviewed-by: Paul Menage <menage@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Pavel Emelyanov <xemul@xxxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/cgroup.h | 1 -
kernel/cgroup.c | 4 ++--
2 files changed, 2 insertions(+), 3 deletions(-)
diff -puN include/linux/cgroup.h~cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu include/linux/cgroup.h
--- a/include/linux/cgroup.h~cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu
+++ a/include/linux/cgroup.h
@@ -337,7 +337,6 @@ struct cgroup_subsys {
#define MAX_CGROUP_TYPE_NAMELEN 32
const char *name;
- /* Protected by RCU */
struct cgroupfs_root *root;
struct list_head sibling;
diff -puN kernel/cgroup.c~cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu kernel/cgroup.c
--- a/kernel/cgroup.c~cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu
+++ a/kernel/cgroup.c
@@ -714,7 +714,7 @@ static int rebind_subsystems(struct cgro
cgrp->subsys[i] = dummytop->subsys[i];
cgrp->subsys[i]->cgroup = cgrp;
list_add(&ss->sibling, &root->subsys_list);
- rcu_assign_pointer(ss->root, root);
+ ss->root = root;
if (ss->bind)
ss->bind(ss, cgrp);
@@ -726,7 +726,7 @@ static int rebind_subsystems(struct cgro
ss->bind(ss, dummytop);
dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL;
- rcu_assign_pointer(subsys[i]->root, &rootnode);
+ subsys[i]->root = &rootnode;
list_del(&ss->sibling);
} else if (bit & final_bits) {
/* Subsystem state should already exist */
_
Patches currently in -mm which might be from laijs@xxxxxxxxxxxxxx are
origin.patch
linux-next.patch
kprobes-bugfix-try_module_get-even-if-calling_mod-is-null.patch
cgroups-add-lock-for-child-cgroups-in-cgroup_post_fork.patch
cgroups-fix-cgroup_iter_next-bug.patch
cgroups-dont-put-struct-cgroupfs_root-protected-by-rcu.patch
cgroups-use-task_lock-for-access-tsk-cgroups-safe-in-cgroup_clone.patch
cgroups-call-find_css_set-safely-in-cgroup_attach_task.patch
devcgroup-use-list_for_each_entry_rcu.patch
memcontrol-rcu_read_lock-to-protect-mm_match_cgroup.patch
cpuset-rcu_read_lock-to-protect-task_cs.patch
cpuset-rcu_read_lock-to-protect-task_cs-even-we-dont-dereference-to-task_css-return-value.patch
--
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