| Message ID | 20211205183220.818872-2-longman@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | cgroup/cpuset: Add new cpuset partition type & empty effecitve cpus | expand |
On Sun, Dec 05, 2021 at 01:32:14PM -0500, Waiman Long wrote: > In validate_change(), there is a check since v2.6.12 to make sure that > each of the child cpusets must be a subset of a parent cpuset. IOW, it > allows child cpusets to restrict what changes can be made to a parent's > "cpuset.cpus". This actually violates one of the core principles of the > default hierarchy where a cgroup higher up in the hierarchy should be > able to change configuration however it sees fit as deligation breaks > down otherwise. > > To address this issue, the check is now removed for the default hierarchy > to free parent cpusets from being restricted by child cpusets. The > check will still apply for legacy hierarchy. > > Suggested-by: Tejun Heo <tj@kernel.org> > Signed-off-by: Waiman Long <longman@redhat.com> Applied to cgroup/for-5.17. Thanks.
On Mon, Dec 13, 2021 at 10:41:23AM -1000, Tejun Heo <tj@kernel.org> wrote: > > To address this issue, the check is now removed for the default hierarchy > > to free parent cpusets from being restricted by child cpusets. The > > check will still apply for legacy hierarchy. I'm trying to find whether something in update_cpumasks_hier() ensures the constraint is checkd on the legacy hierarchy but it seems to me this baby was thrown out with the bathwater. How is the legacy check still applied? > Applied to cgroup/for-5.17. It comes out a bit more complex if I want to achieve both variants in the below followup: diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 0dd7d853ed17..8b6e06f504f6 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -590,6 +590,35 @@ static inline void free_cpuset(struct cpuset *cs) kfree(cs); } +/* + * validate_change_legacy() - Validate conditions specific to legacy (v1) + * behavior. + */ +static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial) +{ + struct cgroup_subsys_state *css; + struct cpuset *c, *par; + int ret; + + WARN_ON_ONCE(!rcu_read_lock_held()); + + /* Each of our child cpusets must be a subset of us */ + ret = -EBUSY; + cpuset_for_each_child(c, css, cur) + if (!is_cpuset_subset(c, trial)) + goto out; + + /* On legacy hierarchy, we must be a subset of our parent cpuset. */ + ret = -EACCES; + par = parent_cs(cur); + if (par && !is_cpuset_subset(trial, par)) + goto out; + + ret = 0; +out: + return ret; +} + /* * validate_change() - Used to validate that any proposed cpuset change * follows the structural rules for cpusets. @@ -614,20 +643,21 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) { struct cgroup_subsys_state *css; struct cpuset *c, *par; - int ret; - - /* The checks don't apply to root cpuset */ - if (cur == &top_cpuset) - return 0; + int ret = 0; rcu_read_lock(); - par = parent_cs(cur); - /* On legacy hierarchy, we must be a subset of our parent cpuset. */ - ret = -EACCES; - if (!is_in_v2_mode() && !is_cpuset_subset(trial, par)) + ret = validate_change_legacy(cur, trial); + if (ret) + goto out; + + /* Remaining checks don't apply to root cpuset */ + ret = 0; + if (cur == &top_cpuset) goto out; + par = parent_cs(cur); + /* * If either I or some sibling (!= me) is exclusive, we can't * overlap @@ -1175,9 +1205,7 @@ enum subparts_cmd { * * Because of the implicit cpu exclusive nature of a partition root, * cpumask changes that violates the cpu exclusivity rule will not be - * permitted when checked by validate_change(). The validate_change() - * function will also prevent any changes to the cpu list if it is not - * a superset of children's cpu lists. + * permitted when checked by validate_change(). */ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd, struct cpumask *newmask,
On 12/15/21 07:23, Michal Koutný wrote: > On Mon, Dec 13, 2021 at 10:41:23AM -1000, Tejun Heo <tj@kernel.org> wrote: >>> To address this issue, the check is now removed for the default hierarchy >>> to free parent cpusets from being restricted by child cpusets. The >>> check will still apply for legacy hierarchy. > I'm trying to find whether something in update_cpumasks_hier() ensures > the constraint is checkd on the legacy hierarchy but it seems to me this > baby was thrown out with the bathwater. How is the legacy check still > applied? Yes, you are right. I did remove the check for legacy hierarchy too. >> Applied to cgroup/for-5.17. > It comes out a bit more complex if I want to achieve both variants in > the below followup: > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 0dd7d853ed17..8b6e06f504f6 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -590,6 +590,35 @@ static inline void free_cpuset(struct cpuset *cs) > kfree(cs); > } > > +/* > + * validate_change_legacy() - Validate conditions specific to legacy (v1) > + * behavior. > + */ > +static int validate_change_legacy(struct cpuset *cur, struct cpuset *trial) > +{ > + struct cgroup_subsys_state *css; > + struct cpuset *c, *par; > + int ret; > + > + WARN_ON_ONCE(!rcu_read_lock_held()); > + > + /* Each of our child cpusets must be a subset of us */ > + ret = -EBUSY; > + cpuset_for_each_child(c, css, cur) > + if (!is_cpuset_subset(c, trial)) > + goto out; > + > + /* On legacy hierarchy, we must be a subset of our parent cpuset. */ > + ret = -EACCES; > + par = parent_cs(cur); > + if (par && !is_cpuset_subset(trial, par)) > + goto out; > + > + ret = 0; > +out: > + return ret; > +} > + > /* > * validate_change() - Used to validate that any proposed cpuset change > * follows the structural rules for cpusets. > @@ -614,20 +643,21 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) > { > struct cgroup_subsys_state *css; > struct cpuset *c, *par; > - int ret; > - > - /* The checks don't apply to root cpuset */ > - if (cur == &top_cpuset) > - return 0; > + int ret = 0; > > rcu_read_lock(); > - par = parent_cs(cur); > > - /* On legacy hierarchy, we must be a subset of our parent cpuset. */ > - ret = -EACCES; > - if (!is_in_v2_mode() && !is_cpuset_subset(trial, par)) I think you still need to guard it with "!is_in_v2_mode()". if (!is_in_v2_mode()) { ret = validate_change_legacy(cur, trial); if (ret) goto out; } > + ret = validate_change_legacy(cur, trial); > + if (ret) > + goto out; > + > + /* Remaining checks don't apply to root cpuset */ > + ret = 0; > + if (cur == &top_cpuset) > goto out; > > + par = parent_cs(cur); > + > /* > * If either I or some sibling (!= me) is exclusive, we can't > * overlap Cheers, Longman
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d0e163a02099..0dd7d853ed17 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -616,19 +616,11 @@ static int validate_change(struct cpuset *cur, struct cpuset *trial) struct cpuset *c, *par; int ret; - rcu_read_lock(); - - /* Each of our child cpusets must be a subset of us */ - ret = -EBUSY; - cpuset_for_each_child(c, css, cur) - if (!is_cpuset_subset(c, trial)) - goto out; - - /* Remaining checks don't apply to root cpuset */ - ret = 0; + /* The checks don't apply to root cpuset */ if (cur == &top_cpuset) - goto out; + return 0; + rcu_read_lock(); par = parent_cs(cur); /* On legacy hierarchy, we must be a subset of our parent cpuset. */
In validate_change(), there is a check since v2.6.12 to make sure that each of the child cpusets must be a subset of a parent cpuset. IOW, it allows child cpusets to restrict what changes can be made to a parent's "cpuset.cpus". This actually violates one of the core principles of the default hierarchy where a cgroup higher up in the hierarchy should be able to change configuration however it sees fit as deligation breaks down otherwise. To address this issue, the check is now removed for the default hierarchy to free parent cpusets from being restricted by child cpusets. The check will still apply for legacy hierarchy. Suggested-by: Tejun Heo <tj@kernel.org> Signed-off-by: Waiman Long <longman@redhat.com> --- kernel/cgroup/cpuset.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-)