The patch titled
Subject: cpusets, cgroups: disallow attaching kthreadd
has been added to the -mm tree. Its filename is
cpusets-cgroups-disallow-attaching-kthreadd.patch
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------------------------------------------------------
From: Mike Galbraith <efault@xxxxxx>
Subject: cpusets, cgroups: disallow attaching kthreadd
Allowing kthreadd to be moved to a non-root group makes no sense, it being
a global resource, and needlessly leads unsuspecting users toward trouble.
1. An RT workqueue worker thread spawned in a task group with no
rt_runtime allocated is not schedulable. Simple user error, but
harmful to the box.
2. A worker thread which acquires PF_THREAD_BOUND can never leave a
cpuset, rendering the cpuset immortal.
Save the user some unexpected trouble, just say no.
Signed-off-by: Mike Galbraith <efault@xxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Acked-by: Paul Menage <paul@xxxxxxxxxxxxxx>
Cc: Tejun Heo <htejun@xxxxxxxxx>
Cc: Li Zefan <lizf@xxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cpuset.c | 6 ++++--
kernel/sched/core.c | 10 ++++++++++
2 files changed, 14 insertions(+), 2 deletions(-)
diff -puN kernel/cpuset.c~cpusets-cgroups-disallow-attaching-kthreadd kernel/cpuset.c
--- a/kernel/cpuset.c~cpusets-cgroups-disallow-attaching-kthreadd
+++ a/kernel/cpuset.c
@@ -59,6 +59,7 @@
#include <linux/mutex.h>
#include <linux/workqueue.h>
#include <linux/cgroup.h>
+#include <linux/kthread.h>
/*
* Workqueue for cpuset related tasks.
@@ -1394,9 +1395,10 @@ static int cpuset_can_attach(struct cgro
* set of allowed nodes is unnecessary. Thus, cpusets are not
* applicable for such threads. This prevents checking for success of
* set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
- * be changed.
+ * be changed. We also disallow attaching kthreadd, to prevent its
+ * child from becoming trapped should it then acquire PF_THREAD_BOUND.
*/
- if (tsk->flags & PF_THREAD_BOUND)
+ if (tsk->flags & PF_THREAD_BOUND || tsk == kthreadd_task)
return -EINVAL;
return 0;
diff -puN kernel/sched/core.c~cpusets-cgroups-disallow-attaching-kthreadd kernel/sched/core.c
--- a/kernel/sched/core.c~cpusets-cgroups-disallow-attaching-kthreadd
+++ a/kernel/sched/core.c
@@ -71,6 +71,7 @@
#include <linux/ftrace.h>
#include <linux/slab.h>
#include <linux/init_task.h>
+#include <linux/kthread.h>
#include <asm/tlb.h>
#include <asm/irq_regs.h>
@@ -7532,6 +7533,15 @@ cpu_cgroup_destroy(struct cgroup_subsys
static int
cpu_cgroup_can_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
+ /*
+ * kthreadd can fork workers for an RT workqueue in a cgroup
+ * which may or may not have rt_runtime allocated. Just say no,
+ * as attaching a global resource to a non-root group doesn't
+ * make any sense anyway.
+ */
+ if (tsk == kthreadd_task)
+ return -EINVAL;
+
#ifdef CONFIG_RT_GROUP_SCHED
if (!sched_rt_can_attach(cgroup_tg(cgrp), tsk))
return -EINVAL;
_
Subject: Subject: cpusets, cgroups: disallow attaching kthreadd
Patches currently in -mm which might be from efault@xxxxxx are
origin.patch
linux-next.patch
cpusets-cgroups-disallow-attaching-kthreadd.patch
ipc-semc-alternatives-to-preempt_disable.patch
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