Patch "cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup-cpuset-make-cpuset_fork-handle-clone_into_cgr.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0cd0e87ceae9b62f8bb13629d42a468ab41a846d
Author: Waiman Long <longman@xxxxxxxxxx>
Date:   Tue Apr 11 09:35:58 2023 -0400

    cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly
    
    [ Upstream commit 42a11bf5c5436e91b040aeb04063be1710bb9f9c ]
    
    By default, the clone(2) syscall spawn a child process into the same
    cgroup as its parent. With the use of the CLONE_INTO_CGROUP flag
    introduced by commit ef2c41cf38a7 ("clone3: allow spawning processes
    into cgroups"), the child will be spawned into a different cgroup which
    is somewhat similar to writing the child's tid into "cgroup.threads".
    
    The current cpuset_fork() method does not properly handle the
    CLONE_INTO_CGROUP case where the cpuset of the child may be different
    from that of its parent.  Update the cpuset_fork() method to treat the
    CLONE_INTO_CGROUP case similar to cpuset_attach().
    
    Since the newly cloned task has not been running yet, its actual
    memory usage isn't known. So it is not necessary to make change to mm
    in cpuset_fork().
    
    Fixes: ef2c41cf38a7 ("clone3: allow spawning processes into cgroups")
    Reported-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
    Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx # v5.7+
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 1c549452c4abb..85f071fb1a414 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2515,16 +2515,33 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)
 }
 
 /*
- * Protected by cpuset_rwsem.  cpus_attach is used only by cpuset_attach()
+ * Protected by cpuset_rwsem. cpus_attach is used only by cpuset_attach_task()
  * but we can't allocate it dynamically there.  Define it global and
  * allocate from cpuset_init().
  */
 static cpumask_var_t cpus_attach;
+static nodemask_t cpuset_attach_nodemask_to;
+
+static void cpuset_attach_task(struct cpuset *cs, struct task_struct *task)
+{
+	percpu_rwsem_assert_held(&cpuset_rwsem);
+
+	if (cs != &top_cpuset)
+		guarantee_online_cpus(task, cpus_attach);
+	else
+		cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
+	/*
+	 * can_attach beforehand should guarantee that this doesn't
+	 * fail.  TODO: have a better way to handle failure here
+	 */
+	WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
+
+	cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
+	cpuset_update_task_spread_flags(cs, task);
+}
 
 static void cpuset_attach(struct cgroup_taskset *tset)
 {
-	/* static buf protected by cpuset_rwsem */
-	static nodemask_t cpuset_attach_nodemask_to;
 	struct task_struct *task;
 	struct task_struct *leader;
 	struct cgroup_subsys_state *css;
@@ -2539,20 +2556,8 @@ static void cpuset_attach(struct cgroup_taskset *tset)
 
 	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
 
-	cgroup_taskset_for_each(task, css, tset) {
-		if (cs != &top_cpuset)
-			guarantee_online_cpus(task, cpus_attach);
-		else
-			cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
-		/*
-		 * can_attach beforehand should guarantee that this doesn't
-		 * fail.  TODO: have a better way to handle failure here
-		 */
-		WARN_ON_ONCE(set_cpus_allowed_ptr(task, cpus_attach));
-
-		cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to);
-		cpuset_update_task_spread_flags(cs, task);
-	}
+	cgroup_taskset_for_each(task, css, tset)
+		cpuset_attach_task(cs, task);
 
 	/*
 	 * Change mm for all threadgroup leaders. This is expensive and may
@@ -3240,11 +3245,28 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
  */
 static void cpuset_fork(struct task_struct *task)
 {
-	if (task_css_is_root(task, cpuset_cgrp_id))
+	struct cpuset *cs;
+	bool same_cs;
+
+	rcu_read_lock();
+	cs = task_cs(task);
+	same_cs = (cs == task_cs(current));
+	rcu_read_unlock();
+
+	if (same_cs) {
+		if (cs == &top_cpuset)
+			return;
+
+		set_cpus_allowed_ptr(task, current->cpus_ptr);
+		task->mems_allowed = current->mems_allowed;
 		return;
+	}
 
-	set_cpus_allowed_ptr(task, current->cpus_ptr);
-	task->mems_allowed = current->mems_allowed;
+	/* CLONE_INTO_CGROUP */
+	percpu_down_write(&cpuset_rwsem);
+	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
+	cpuset_attach_task(cs, task);
+	percpu_up_write(&cpuset_rwsem);
 }
 
 struct cgroup_subsys cpuset_cgrp_subsys = {



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