From: David Rientjes <rientjes@google.com>
Date: Thu, 5 Jun 2008 19:57:11 +0000 (-0700)
Subject: sched: prevent bound kthreads from changing cpus_allowed
X-Git-Tag: v2.6.27-rc1~1105^2~55
X-Git-Url: http://www.pilppa.org/gitweb/gitweb.cgi?p=linux-2.6-omap-h63xx.git;a=commitdiff_plain;h=9985b0bab332289f14837eff3c6e0bcc658b58f7

sched: prevent bound kthreads from changing cpus_allowed

Kthreads that have called kthread_bind() are bound to specific cpus, so
other tasks should not be able to change their cpus_allowed from under
them.  Otherwise, it is possible to move kthreads, such as the migration
or software watchdog threads, so they are not allowed access to the cpu
they work on.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Menage <menage@google.com>
Cc: Paul Jackson <pj@sgi.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d25acf600a3..2db1485f865 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1486,6 +1486,7 @@ 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_THREAD_BOUND	0x04000000	/* Thread 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
index 6090d18b58a..b84354f4de3 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1190,6 +1190,15 @@ static int cpuset_can_attach(struct cgroup_subsys *ss,
 
 	if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
 		return -ENOSPC;
+	if (tsk->flags & PF_THREAD_BOUND) {
+		cpumask_t mask;
+
+		mutex_lock(&callback_mutex);
+		mask = cs->cpus_allowed;
+		mutex_unlock(&callback_mutex);
+		if (!cpus_equal(tsk->cpus_allowed, mask))
+			return -EINVAL;
+	}
 
 	return security_task_setscheduler(tsk, 0, NULL);
 }
@@ -1203,11 +1212,14 @@ 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 err;
 
 	mutex_lock(&callback_mutex);
 	guarantee_online_cpus(cs, &cpus);
-	set_cpus_allowed_ptr(tsk, &cpus);
+	err = set_cpus_allowed_ptr(tsk, &cpus);
 	mutex_unlock(&callback_mutex);
+	if (err)
+		return;
 
 	from = oldcs->mems_allowed;
 	to = cs->mems_allowed;
diff --git a/kernel/kthread.c b/kernel/kthread.c
index bd1b9ea024e..97747cdd37c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -180,6 +180,7 @@ void kthread_bind(struct task_struct *k, unsigned int cpu)
 	set_task_cpu(k, cpu);
 	k->cpus_allowed = cpumask_of_cpu(cpu);
 	k->rt.nr_cpus_allowed = 1;
+	k->flags |= PF_THREAD_BOUND;
 }
 EXPORT_SYMBOL(kthread_bind);
 
diff --git a/kernel/sched.c b/kernel/sched.c
index e9c24a12865..164fe7fe0d8 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5563,6 +5563,12 @@ int set_cpus_allowed_ptr(struct task_struct *p, const cpumask_t *new_mask)
 		goto out;
 	}
 
+	if (unlikely((p->flags & PF_THREAD_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 {