The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x eee87853794187f6adbe19533ed79c8b44b36a91 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2023041703-wildland-privacy-e6d6@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

eee878537941 ("cgroup/cpuset: Add cpuset_can_fork() and cpuset_cancel_fork() methods") 42a11bf5c543 ("cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly") 18f9a4d47527 ("cgroup/cpuset: Skip spread flags update on v2") e2d59900d936 ("cgroup/cpuset: Allow no-task partition to have empty cpuset.cpus.effective") 18065ebe9b33 ("cgroup/cpuset: Miscellaneous cleanups & add helper functions") f9da322e864e ("cgroup: cleanup comments") 8ca1b5a49885 ("mm/page_alloc: detect allocation forbidden by cpuset and bail out early")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From eee87853794187f6adbe19533ed79c8b44b36a91 Mon Sep 17 00:00:00 2001 From: Waiman Long longman@redhat.com Date: Tue, 11 Apr 2023 09:35:59 -0400 Subject: [PATCH] cgroup/cpuset: Add cpuset_can_fork() and cpuset_cancel_fork() methods MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit

In the case of CLONE_INTO_CGROUP, not all cpusets are ready to accept new tasks. It is too late to check that in cpuset_fork(). So we need to add the cpuset_can_fork() and cpuset_cancel_fork() methods to pre-check it before we can allow attachment to a different cpuset.

We also need to set the attach_in_progress flag to alert other code that a new task is going to be added to the cpuset.

Fixes: ef2c41cf38a7 ("clone3: allow spawning processes into cgroups") Suggested-by: Michal Koutný mkoutny@suse.com Signed-off-by: Waiman Long longman@redhat.com Cc: stable@vger.kernel.org # v5.7+ Signed-off-by: Tejun Heo tj@kernel.org

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 2ccfae74acf9..166a45019f66 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2453,6 +2453,20 @@ static int fmeter_getrate(struct fmeter *fmp)

static struct cpuset *cpuset_attach_old_cs;

+/* + * Check to see if a cpuset can accept a new task + * For v1, cpus_allowed and mems_allowed can't be empty. + * For v2, effective_cpus can't be empty. + * Note that in v1, effective_cpus = cpus_allowed. + */ +static int cpuset_can_attach_check(struct cpuset *cs) +{ + if (cpumask_empty(cs->effective_cpus) || + (!is_in_v2_mode() && nodes_empty(cs->mems_allowed))) + return -ENOSPC; + return 0; +} + /* Called by cgroups to determine if a cpuset is usable; cpuset_rwsem held */ static int cpuset_can_attach(struct cgroup_taskset *tset) { @@ -2467,16 +2481,9 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)

percpu_down_write(&cpuset_rwsem);

- /* allow moving tasks into an empty cpuset if on default hierarchy */ - ret = -ENOSPC; - if (!is_in_v2_mode() && - (cpumask_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))) - goto out_unlock; - - /* - * Task cannot be moved to a cpuset with empty effective cpus. - */ - if (cpumask_empty(cs->effective_cpus)) + /* Check to see if task is allowed in the cpuset */ + ret = cpuset_can_attach_check(cs); + if (ret) goto out_unlock;

cgroup_taskset_for_each(task, css, tset) { @@ -2493,7 +2500,6 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) * changes which zero cpus/mems_allowed. */ cs->attach_in_progress++; - ret = 0; out_unlock: percpu_up_write(&cpuset_rwsem); return ret; @@ -3264,6 +3270,68 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css) percpu_up_write(&cpuset_rwsem); }

+/* + * In case the child is cloned into a cpuset different from its parent, + * additional checks are done to see if the move is allowed. + */ +static int cpuset_can_fork(struct task_struct *task, struct css_set *cset) +{ + struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]); + bool same_cs; + int ret; + + rcu_read_lock(); + same_cs = (cs == task_cs(current)); + rcu_read_unlock(); + + if (same_cs) + return 0; + + lockdep_assert_held(&cgroup_mutex); + percpu_down_write(&cpuset_rwsem); + + /* Check to see if task is allowed in the cpuset */ + ret = cpuset_can_attach_check(cs); + if (ret) + goto out_unlock; + + ret = task_can_attach(task, cs->effective_cpus); + if (ret) + goto out_unlock; + + ret = security_task_setscheduler(task); + if (ret) + goto out_unlock; + + /* + * Mark attach is in progress. This makes validate_change() fail + * changes which zero cpus/mems_allowed. + */ + cs->attach_in_progress++; +out_unlock: + percpu_up_write(&cpuset_rwsem); + return ret; +} + +static void cpuset_cancel_fork(struct task_struct *task, struct css_set *cset) +{ + struct cpuset *cs = css_cs(cset->subsys[cpuset_cgrp_id]); + bool same_cs; + + rcu_read_lock(); + same_cs = (cs == task_cs(current)); + rcu_read_unlock(); + + if (same_cs) + return; + + percpu_down_write(&cpuset_rwsem); + cs->attach_in_progress--; + if (!cs->attach_in_progress) + wake_up(&cpuset_attach_wq); + percpu_up_write(&cpuset_rwsem); +} + /* * Make sure the new task conform to the current state of its parent, * which could have been changed by cpuset just after it inherits the @@ -3292,6 +3360,11 @@ static void cpuset_fork(struct task_struct *task) percpu_down_write(&cpuset_rwsem); guarantee_online_mems(cs, &cpuset_attach_nodemask_to); cpuset_attach_task(cs, task); + + cs->attach_in_progress--; + if (!cs->attach_in_progress) + wake_up(&cpuset_attach_wq); + percpu_up_write(&cpuset_rwsem); }

@@ -3305,6 +3378,8 @@ struct cgroup_subsys cpuset_cgrp_subsys = { .attach = cpuset_attach, .post_attach = cpuset_post_attach, .bind = cpuset_bind, + .can_fork = cpuset_can_fork, + .cancel_fork = cpuset_cancel_fork, .fork = cpuset_fork, .legacy_cftypes = legacy_files, .dfl_cftypes = dfl_files,