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SubjectRe: [RFC/PATCH 0/4] CPUSET driven CPU isolation
On Thu, 28 Feb 2008, David Rientjes wrote:

> Should the kernel refuse to move some threads, such as the migration
> or watchdog kthreads, out of the root cpuset where the mems can be
> adjusted to disallow access to the cpu to which they are bound? This is
> a quick way to cause a crash or soft lockup.
>

Something like this?
---
include/linux/sched.h | 1 +
kernel/cpuset.c | 5 ++++-
kernel/kthread.c | 1 +
kernel/sched.c | 6 ++++++
4 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1464,6 +1464,7 @@ static inline void put_task_struct(struct task_struct *t)
#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
#define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */
#define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */
+#define PF_CPU_BOUND 0x04000000 /* Kthread bound to specific cpu */
#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
#define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezeable */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1175,11 +1175,14 @@ static void cpuset_attach(struct cgroup_subsys *ss,
struct mm_struct *mm;
struct cpuset *cs = cgroup_cs(cont);
struct cpuset *oldcs = cgroup_cs(oldcont);
+ int ret;

mutex_lock(&callback_mutex);
guarantee_online_cpus(cs, &cpus);
- set_cpus_allowed(tsk, cpus);
+ ret = set_cpus_allowed(tsk, cpus);
mutex_unlock(&callback_mutex);
+ if (ret < 0)
+ return;

from = oldcs->mems_allowed;
to = cs->mems_allowed;
diff --git a/kernel/kthread.c b/kernel/kthread.c
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -180,6 +180,7 @@ void kthread_bind(struct task_struct *k, unsigned int cpu)
wait_task_inactive(k);
set_task_cpu(k, cpu);
k->cpus_allowed = cpumask_of_cpu(cpu);
+ k->flags |= PF_CPU_BOUND;
}
EXPORT_SYMBOL(kthread_bind);

diff --git a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5345,6 +5345,12 @@ int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask)
goto out;
}

+ if (unlikely((p->flags & PF_CPU_BOUND) && p != current &&
+ !cpus_equal(p->cpus_allowed, new_mask))) {
+ ret = -EINVAL;
+ goto out;
+ }
+
if (p->sched_class->set_cpus_allowed)
p->sched_class->set_cpus_allowed(p, &new_mask);
else {

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