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 d25acf6..2db1485 100644 (file)
--- 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 6090d18..b84354f 100644 (file)
--- 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 bd1b9ea..97747cd 100644 (file)
--- 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 e9c24a1..164fe7f 100644 (file)
--- 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 {