| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <8ed8cac1-4cf1-4880-9e7d-4e8c816797fa@redhat.com>
Date: Tue, 12 Aug 2025 21:33:39 -0400
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, Waiman Long <llong@...hat.com>,
tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com, mingo@...hat.com,
peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, vschneid@...hat.com
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
lujialin4@...wei.com, chenridong@...wei.com
Subject: Re: [PATCH -next 1/4] cpuset: remove redundant CS_ONLINE flag
On 8/12/25 9:20 PM, Chen Ridong wrote:
>
> On 2025/8/13 9:00, Waiman Long wrote:
>> On 8/12/25 8:54 PM, Chen Ridong wrote:
>>> On 2025/8/12 22:44, Waiman Long wrote:
>>>> On 8/8/25 5:25 AM, Chen Ridong wrote:
>>>>> From: Chen Ridong <chenridong@...wei.com>
>>>>>
>>>>> The CS_ONLINE flag was introduced prior to the CSS_ONLINE flag in the
>>>>> cpuset subsystem. Currently, the flag setting sequence is as follows:
>>>>>
>>>>> 1. cpuset_css_online() sets CS_ONLINE
>>>>> 2. css->flags gets CSS_ONLINE set
>>>>> ...
>>>>> 3. cgroup->kill_css sets CSS_DYING
>>>>> 4. cpuset_css_offline() clears CS_ONLINE
>>>>> 5. css->flags clears CSS_ONLINE
>>>>>
>>>>> The is_cpuset_online() check currently occurs between steps 1 and 3.
>>>>> However, it would be equally safe to perform this check between steps 2
>>>>> and 3, as CSS_ONLINE provides the same synchronization guarantee as
>>>>> CS_ONLINE.
>>>>>
>>>>> Since CS_ONLINE is redundant with CSS_ONLINE and provides no additional
>>>>> synchronization benefits, we can safely remove it to simplify the code.
>>>>>
>>>>> Signed-off-by: Chen Ridong <chenridong@...wei.com>
>>>>> ---
>>>>> include/linux/cgroup.h | 5 +++++
>>>>> kernel/cgroup/cpuset-internal.h | 3 +--
>>>>> kernel/cgroup/cpuset.c | 4 +---
>>>>> 3 files changed, 7 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
>>>>> index b18fb5fcb38e..ae73dbb19165 100644
>>>>> --- a/include/linux/cgroup.h
>>>>> +++ b/include/linux/cgroup.h
>>>>> @@ -354,6 +354,11 @@ static inline bool css_is_dying(struct cgroup_subsys_state *css)
>>>>> return css->flags & CSS_DYING;
>>>>> }
>>>>> +static inline bool css_is_online(struct cgroup_subsys_state *css)
>>>>> +{
>>>>> + return css->flags & CSS_ONLINE;
>>>>> +}
>>>>> +
>>>>> static inline bool css_is_self(struct cgroup_subsys_state *css)
>>>>> {
>>>>> if (css == &css->cgroup->self) {
>>>>> diff --git a/kernel/cgroup/cpuset-internal.h b/kernel/cgroup/cpuset-internal.h
>>>>> index 383963e28ac6..75b3aef39231 100644
>>>>> --- a/kernel/cgroup/cpuset-internal.h
>>>>> +++ b/kernel/cgroup/cpuset-internal.h
>>>>> @@ -38,7 +38,6 @@ enum prs_errcode {
>>>>> /* bits in struct cpuset flags field */
>>>>> typedef enum {
>>>>> - CS_ONLINE,
>>>>> CS_CPU_EXCLUSIVE,
>>>>> CS_MEM_EXCLUSIVE,
>>>>> CS_MEM_HARDWALL,
>>>>> @@ -202,7 +201,7 @@ static inline struct cpuset *parent_cs(struct cpuset *cs)
>>>>> /* convenient tests for these bits */
>>>>> static inline bool is_cpuset_online(struct cpuset *cs)
>>>>> {
>>>>> - return test_bit(CS_ONLINE, &cs->flags) && !css_is_dying(&cs->css);
>>>>> + return css_is_online(&cs->css) && !css_is_dying(&cs->css);
>>>>> }
>>>>> static inline int is_cpu_exclusive(const struct cpuset *cs)
>>>>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>>>>> index f74d04429a29..cf7cd2255265 100644
>>>>> --- a/kernel/cgroup/cpuset.c
>>>>> +++ b/kernel/cgroup/cpuset.c
>>>>> @@ -207,7 +207,7 @@ static inline void notify_partition_change(struct cpuset *cs, int old_prs)
>>>>> * parallel, we may leave an offline CPU in cpu_allowed or some other masks.
>>>>> */
>>>>> static struct cpuset top_cpuset = {
>>>>> - .flags = BIT(CS_ONLINE) | BIT(CS_CPU_EXCLUSIVE) |
>>>>> + .flags = BIT(CS_CPU_EXCLUSIVE) |
>>>>> BIT(CS_MEM_EXCLUSIVE) | BIT(CS_SCHED_LOAD_BALANCE),
>>>>> .partition_root_state = PRS_ROOT,
>>>>> .relax_domain_level = -1,
>>>> top_cpuset.css is not initialized like the one in the children. If you modify is_cpuset_online() to
>>>> test the css.flags, you will probably need to set the CSS_ONLINE flag in top_cpuset.css.flags. I do
>>>> doubt that we will apply the is_cpuset_online() test on top_cpuset. To be consistent, we should
>>>> support that.
>>>>
>>>> BTW, other statically allocated css'es in the cgroup root may have similar problem. If you make the
>>>> css_is_online() helper available to all other controllers, you will have to document that
>>>> limitation.
>>>>
>>>> Cheers,
>>>> Longman
>>> Hi, Longman, thank you for your response.
>>>
>>> If I understand correctly, the CSS_ONLINE flag should be set in top_cpuset.css during the following
>>> process:
>>>
>>> css_create
>>> css = ss->css_alloc(parent_css); // cgroup root is static, unlike children
>>> online_css(css);
>>> ret = ss->css_online(css); // css root may differ from children
>>> css->flags |= CSS_ONLINE; // css.flags is set with CSS_ONLINE, including the root css
>>>
>>> I think css online must be successful, and it's CSS_ONLINE flag must be set. Do I missing anything?
>> I am talking about just the top_cpuset which is statically allocated. It is not created by the
>> css_create() call and so the CSS_ONLINE will not be set.
>>
>> Cheers,
>> Longman
> Hi Longman,
>
> Apologies for the call stack earlier. Thank you for your patience in clarifying this matter.
>
> The CSS root is brought online through the following initialization flow:
>
> cgroup_init_subsys
> css = ss->css_alloc(NULL); // css root is static, unlike children
> online_css(css)
> ret = ss->css_online(css); // css root may differ from children
> css->flags |= CSS_ONLINE; // css.flags is set with CSS_ONLINE, including the root css
>
> My key point is that:
> - The root CSS should be online by design.
> - Root css CSS_ONLINE flag should be properly set during initialization.
Yes, you are right. I missed css_online() call for the root css for each
controller. Thanks for the clarification.
With that, I am OK with this patch. Though the other ones are not good.
Acked-by: Waiman Long <longman@...hat.com>
Powered by blists - more mailing lists