Re: [RFC/PATCH 0/4] CPUSET driven CPU isolation

[David Rientjes]

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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