* [PATCH] cpuset: rcu_read_lock() to protect task_cs()
@ 2008-11-21 8:49 Lai Jiangshan
2008-11-21 18:36 ` Paul Menage
[not found] ` <49267621.2070706-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
0 siblings, 2 replies; 4+ messages in thread
From: Lai Jiangshan @ 2008-11-21 8:49 UTC (permalink / raw)
To: Andrew Morton, Paul Menage, Linux Kernel Mailing List,
Linux Containers
task_cs() calls cgroup_subsys_state().
we must use rcu_read_lock() to protect cgroup_subsys_state().
it's correct that top_cpuset is never freed, but cgroup_subsys_state()
accesses css_set, this css_set maybe freed when task_cs() called.
we use use rcu_read_lock() to protect it.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3e00526..e0e087e 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void)
struct task_struct *tsk = current;
struct cpuset *cs;
- if (task_cs(tsk) == &top_cpuset) {
- /* Don't need rcu for top_cpuset. It's never freed. */
- my_cpusets_mem_gen = top_cpuset.mems_generation;
- } else {
- rcu_read_lock();
- my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
- rcu_read_unlock();
- }
+ rcu_read_lock();
+ my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
+ rcu_read_unlock();
if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
mutex_lock(&callback_mutex);
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH] cpuset: rcu_read_lock() to protect task_cs()
@ 2008-11-21 8:49 Lai Jiangshan
0 siblings, 0 replies; 4+ messages in thread
From: Lai Jiangshan @ 2008-11-21 8:49 UTC (permalink / raw)
To: Andrew Morton, Paul Menage, Linux Kernel Mailing List,
Linux Containers
task_cs() calls cgroup_subsys_state().
we must use rcu_read_lock() to protect cgroup_subsys_state().
it's correct that top_cpuset is never freed, but cgroup_subsys_state()
accesses css_set, this css_set maybe freed when task_cs() called.
we use use rcu_read_lock() to protect it.
Signed-off-by: Lai Jiangshan <laijs-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
---
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3e00526..e0e087e 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void)
struct task_struct *tsk = current;
struct cpuset *cs;
- if (task_cs(tsk) == &top_cpuset) {
- /* Don't need rcu for top_cpuset. It's never freed. */
- my_cpusets_mem_gen = top_cpuset.mems_generation;
- } else {
- rcu_read_lock();
- my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
- rcu_read_unlock();
- }
+ rcu_read_lock();
+ my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
+ rcu_read_unlock();
if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) {
mutex_lock(&callback_mutex);
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] cpuset: rcu_read_lock() to protect task_cs()
[not found] ` <49267621.2070706-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
@ 2008-11-21 18:36 ` Paul Menage
0 siblings, 0 replies; 4+ messages in thread
From: Paul Menage @ 2008-11-21 18:36 UTC (permalink / raw)
To: Lai Jiangshan; +Cc: Linux Containers, Andrew Morton, Linux Kernel Mailing List
On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org> wrote:
>
> task_cs() calls cgroup_subsys_state().
You mean it calls task_subsys_state().
>
> we must use rcu_read_lock() to protect cgroup_subsys_state().
>
> it's correct that top_cpuset is never freed, but cgroup_subsys_state()
> accesses css_set, this css_set maybe freed when task_cs() called.
It would be nice to have an RCU debug mode where rcu_dereference()
does a WARN() if it's invoked not under rcu_read_lock().
>
> we use use rcu_read_lock() to protect it.
>
> Signed-off-by: Lai Jiangshan <laijs-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
> ---
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 3e00526..e0e087e 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void)
> struct task_struct *tsk = current;
> struct cpuset *cs;
>
> - if (task_cs(tsk) == &top_cpuset) {
> - /* Don't need rcu for top_cpuset. It's never freed. */
> - my_cpusets_mem_gen = top_cpuset.mems_generation;
> - } else {
> - rcu_read_lock();
> - my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> - rcu_read_unlock();
> - }
> + rcu_read_lock();
> + my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> + rcu_read_unlock();
Yes, I guess this old cpusets assumption is no longer valid in cgroups.
Acked-by: Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Thanks
Paul
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] cpuset: rcu_read_lock() to protect task_cs()
2008-11-21 8:49 [PATCH] cpuset: rcu_read_lock() to protect task_cs() Lai Jiangshan
@ 2008-11-21 18:36 ` Paul Menage
[not found] ` <49267621.2070706-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
1 sibling, 0 replies; 4+ messages in thread
From: Paul Menage @ 2008-11-21 18:36 UTC (permalink / raw)
To: Lai Jiangshan; +Cc: Andrew Morton, Linux Kernel Mailing List, Linux Containers
On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@cn.fujitsu.com> wrote:
>
> task_cs() calls cgroup_subsys_state().
You mean it calls task_subsys_state().
>
> we must use rcu_read_lock() to protect cgroup_subsys_state().
>
> it's correct that top_cpuset is never freed, but cgroup_subsys_state()
> accesses css_set, this css_set maybe freed when task_cs() called.
It would be nice to have an RCU debug mode where rcu_dereference()
does a WARN() if it's invoked not under rcu_read_lock().
>
> we use use rcu_read_lock() to protect it.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 3e00526..e0e087e 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void)
> struct task_struct *tsk = current;
> struct cpuset *cs;
>
> - if (task_cs(tsk) == &top_cpuset) {
> - /* Don't need rcu for top_cpuset. It's never freed. */
> - my_cpusets_mem_gen = top_cpuset.mems_generation;
> - } else {
> - rcu_read_lock();
> - my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> - rcu_read_unlock();
> - }
> + rcu_read_lock();
> + my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> + rcu_read_unlock();
Yes, I guess this old cpusets assumption is no longer valid in cgroups.
Acked-by: Paul Menage <menage@google.com>
Thanks
Paul
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2008-11-21 18:36 UTC | newest]
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2008-11-21 8:49 [PATCH] cpuset: rcu_read_lock() to protect task_cs() Lai Jiangshan
2008-11-21 18:36 ` Paul Menage
[not found] ` <49267621.2070706-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
2008-11-21 18:36 ` Paul Menage
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2008-11-21 8:49 Lai Jiangshan
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