sched: Fix balance vs hotplug race

Since (e761b77: cpu hotplug, sched: Introduce cpu_active_map and redo
sched domain managment) we have cpu_active_mask which is suppose to rule
scheduler migration and load-balancing, except it never (fully) did.

The particular problem being solved here is a crash in try_to_wake_up()
where select_task_rq() ends up selecting an offline cpu because
select_task_rq_fair() trusts the sched_domain tree to reflect the
current state of affairs, similarly select_task_rq_rt() trusts the
root_domain.

However, the sched_domains are updated from CPU_DEAD, which is after the
cpu is taken offline and after stop_machine is done. Therefore it can
race perfectly well with code assuming the domains are right.

Cure this by building the domains from cpu_active_mask on
CPU_DOWN_PREPARE.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 789cf5f920ce80e697ca05a9a7fde743cdde9e1a..d77b54733c5b63980c51fe354ee91de1a41ce81a 100644 (file)
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -84,6 +84,7 @@ extern const struct cpumask *const cpu_active_mask;
 #define num_online_cpus()      cpumask_weight(cpu_online_mask)
 #define num_possible_cpus()    cpumask_weight(cpu_possible_mask)
 #define num_present_cpus()     cpumask_weight(cpu_present_mask)
+#define num_active_cpus()      cpumask_weight(cpu_active_mask)
 #define cpu_online(cpu)                cpumask_test_cpu((cpu), cpu_online_mask)
 #define cpu_possible(cpu)      cpumask_test_cpu((cpu), cpu_possible_mask)
 #define cpu_present(cpu)       cpumask_test_cpu((cpu), cpu_present_mask)
@@ -92,6 +93,7 @@ extern const struct cpumask *const cpu_active_mask;
 #define num_online_cpus()      1
 #define num_possible_cpus()    1
 #define num_present_cpus()     1
+#define num_active_cpus()      1
 #define cpu_online(cpu)                ((cpu) == 0)
 #define cpu_possible(cpu)      ((cpu) == 0)
 #define cpu_present(cpu)       ((cpu) == 0)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ba0f1ecb21230de60f6ab9fd7b2f58907b48d55..b21688640377494e659f9deaadfb15dca2fe8c06 100644 (file)
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -212,6 +212,8 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
        err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
                                        hcpu, -1, &nr_calls);
        if (err == NOTIFY_BAD) {
+               set_cpu_active(cpu, true);
+
                nr_calls--;
                __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
                                          hcpu, nr_calls, NULL);
@@ -223,11 +225,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 
        /* Ensure that we are not runnable on dying cpu */
        cpumask_copy(old_allowed, &current->cpus_allowed);
-       set_cpus_allowed_ptr(current,
-                            cpumask_of(cpumask_any_but(cpu_online_mask, cpu)));
+       set_cpus_allowed_ptr(current, cpu_active_mask);
 
        err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
        if (err) {
+               set_cpu_active(cpu, true);
                /* CPU didn't die: tell everyone.  Can't complain. */
                if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
                                            hcpu) == NOTIFY_BAD)
@@ -292,9 +294,6 @@ int __ref cpu_down(unsigned int cpu)
 
        err = _cpu_down(cpu, 0);
 
-       if (cpu_online(cpu))
-               set_cpu_active(cpu, true);
-
 out:
        cpu_maps_update_done();
        stop_machine_destroy();
@@ -387,6 +386,15 @@ int disable_nonboot_cpus(void)
         * with the userspace trying to use the CPU hotplug at the same time
         */
        cpumask_clear(frozen_cpus);
+
+       for_each_online_cpu(cpu) {
+               if (cpu == first_cpu)
+                       continue;
+               set_cpu_active(cpu, false);
+       }
+
+       synchronize_sched();
+
        printk("Disabling non-boot CPUs ...\n");
        for_each_online_cpu(cpu) {
                if (cpu == first_cpu)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 43fb7e8000284bd05784ce5f30714e46075ef218..ba401fab459f94a42010f6175b2b69c490920645 100644 (file)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -872,7 +872,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
                if (retval < 0)
                        return retval;
 
-               if (!cpumask_subset(trialcs->cpus_allowed, cpu_online_mask))
+               if (!cpumask_subset(trialcs->cpus_allowed, cpu_active_mask))
                        return -EINVAL;
        }
        retval = validate_change(cs, trialcs);
@@ -2010,7 +2010,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
                }
 
                /* Continue past cpusets with all cpus, mems online */
-               if (cpumask_subset(cp->cpus_allowed, cpu_online_mask) &&
+               if (cpumask_subset(cp->cpus_allowed, cpu_active_mask) &&
                    nodes_subset(cp->mems_allowed, node_states[N_HIGH_MEMORY]))
                        continue;
 
@@ -2019,7 +2019,7 @@ static void scan_for_empty_cpusets(struct cpuset *root)
                /* Remove offline cpus and mems from this cpuset. */
                mutex_lock(&callback_mutex);
                cpumask_and(cp->cpus_allowed, cp->cpus_allowed,
-                           cpu_online_mask);
+                           cpu_active_mask);
                nodes_and(cp->mems_allowed, cp->mems_allowed,
                                                node_states[N_HIGH_MEMORY]);
                mutex_unlock(&callback_mutex);
@@ -2057,8 +2057,10 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
        switch (phase) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
-       case CPU_DEAD:
-       case CPU_DEAD_FROZEN:
+       case CPU_DOWN_PREPARE:
+       case CPU_DOWN_PREPARE_FROZEN:
+       case CPU_DOWN_FAILED:
+       case CPU_DOWN_FAILED_FROZEN:
                break;
 
        default:
@@ -2067,7 +2069,7 @@ static int cpuset_track_online_cpus(struct notifier_block *unused_nb,
 
        cgroup_lock();
        mutex_lock(&callback_mutex);
-       cpumask_copy(top_cpuset.cpus_allowed, cpu_online_mask);
+       cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
        mutex_unlock(&callback_mutex);
        scan_for_empty_cpusets(&top_cpuset);
        ndoms = generate_sched_domains(&doms, &attr);
@@ -2114,7 +2116,7 @@ static int cpuset_track_online_nodes(struct notifier_block *self,
 
 void __init cpuset_init_smp(void)
 {
-       cpumask_copy(top_cpuset.cpus_allowed, cpu_online_mask);
+       cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
        top_cpuset.mems_allowed = node_states[N_HIGH_MEMORY];
 
        hotcpu_notifier(cpuset_track_online_cpus, 0);

diff --git a/kernel/sched.c b/kernel/sched.c
index aa31244caa9f2f4170eba50797c011401f73276e..281da29d080192c8924d444eed5fc75adacf5492 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4134,7 +4134,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
        unsigned long flags;
        struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
 
-       cpumask_copy(cpus, cpu_online_mask);
+       cpumask_copy(cpus, cpu_active_mask);
 
        /*
         * When power savings policy is enabled for the parent domain, idle
@@ -4297,7 +4297,7 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd)
        int all_pinned = 0;
        struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
 
-       cpumask_copy(cpus, cpu_online_mask);
+       cpumask_copy(cpus, cpu_active_mask);
 
        /*
         * When power savings policy is enabled for the parent domain, idle
@@ -4694,7 +4694,7 @@ int select_nohz_load_balancer(int stop_tick)
                cpumask_set_cpu(cpu, nohz.cpu_mask);
 
                /* time for ilb owner also to sleep */
-               if (cpumask_weight(nohz.cpu_mask) == num_online_cpus()) {
+               if (cpumask_weight(nohz.cpu_mask) == num_active_cpus()) {
                        if (atomic_read(&nohz.load_balancer) == cpu)
                                atomic_set(&nohz.load_balancer, -1);
                        return 0;
@@ -7093,7 +7093,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
        int ret = 0;
 
        rq = task_rq_lock(p, &flags);
-       if (!cpumask_intersects(new_mask, cpu_online_mask)) {
+       if (!cpumask_intersects(new_mask, cpu_active_mask)) {
                ret = -EINVAL;
                goto out;
        }
@@ -7115,7 +7115,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
        if (cpumask_test_cpu(task_cpu(p), new_mask))
                goto out;
 
-       if (migrate_task(p, cpumask_any_and(cpu_online_mask, new_mask), &req)) {
+       if (migrate_task(p, cpumask_any_and(cpu_active_mask, new_mask), &req)) {
                /* Need help from migration thread: drop lock and wait. */
                struct task_struct *mt = rq->migration_thread;
 
@@ -7269,19 +7269,19 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)
 
 again:
        /* Look for allowed, online CPU in same node. */
-       for_each_cpu_and(dest_cpu, nodemask, cpu_online_mask)
+       for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask)
                if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))
                        goto move;
 
        /* Any allowed, online CPU? */
-       dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);
+       dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);
        if (dest_cpu < nr_cpu_ids)
                goto move;
 
        /* No more Mr. Nice Guy. */
        if (dest_cpu >= nr_cpu_ids) {
                cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
-               dest_cpu = cpumask_any_and(cpu_online_mask, &p->cpus_allowed);
+               dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed);
 
                /*
                 * Don't tell them about moving exiting tasks or
@@ -7310,7 +7310,7 @@ move:
  */
 static void migrate_nr_uninterruptible(struct rq *rq_src)
 {
-       struct rq *rq_dest = cpu_rq(cpumask_any(cpu_online_mask));
+       struct rq *rq_dest = cpu_rq(cpumask_any(cpu_active_mask));
        unsigned long flags;
 
        local_irq_save(flags);
@@ -7564,7 +7564,7 @@ static ctl_table *sd_alloc_ctl_cpu_table(int cpu)
 static struct ctl_table_header *sd_sysctl_header;
 static void register_sched_domain_sysctl(void)
 {
-       int i, cpu_num = num_online_cpus();
+       int i, cpu_num = num_possible_cpus();
        struct ctl_table *entry = sd_alloc_ctl_entry(cpu_num + 1);
        char buf[32];
 
@@ -7574,7 +7574,7 @@ static void register_sched_domain_sysctl(void)
        if (entry == NULL)
                return;
 
-       for_each_online_cpu(i) {
+       for_each_possible_cpu(i) {
                snprintf(buf, 32, "cpu%d", i);
                entry->procname = kstrdup(buf, GFP_KERNEL);
                entry->mode = 0555;
@@ -9100,7 +9100,7 @@ match1:
        if (doms_new == NULL) {
                ndoms_cur = 0;
                doms_new = &fallback_doms;
-               cpumask_andnot(doms_new[0], cpu_online_mask, cpu_isolated_map);
+               cpumask_andnot(doms_new[0], cpu_active_mask, cpu_isolated_map);
                WARN_ON_ONCE(dattr_new);
        }
 
@@ -9231,8 +9231,10 @@ static int update_sched_domains(struct notifier_block *nfb,
        switch (action) {
        case CPU_ONLINE:
        case CPU_ONLINE_FROZEN:
-       case CPU_DEAD:
-       case CPU_DEAD_FROZEN:
+       case CPU_DOWN_PREPARE:
+       case CPU_DOWN_PREPARE_FROZEN:
+       case CPU_DOWN_FAILED:
+       case CPU_DOWN_FAILED_FROZEN:
                partition_sched_domains(1, NULL, NULL);
                return NOTIFY_OK;
 
@@ -9279,7 +9281,7 @@ void __init sched_init_smp(void)
 #endif
        get_online_cpus();
        mutex_lock(&sched_domains_mutex);
-       arch_init_sched_domains(cpu_online_mask);
+       arch_init_sched_domains(cpu_active_mask);
        cpumask_andnot(non_isolated_cpus, cpu_possible_mask, cpu_isolated_map);
        if (cpumask_empty(non_isolated_cpus))
                cpumask_set_cpu(smp_processor_id(), non_isolated_cpus);