Prev: [PATCH 12/43] workqueue: merge feature parameters into flags
Next: [PATCH 09/43] acpi: use queue_work_on() instead of binding workqueue worker to cpu0
From: Tejun Heo on 26 Feb 2010 07:20
If called after sched_class chooses a CPU which isn't in a task's
cpus_allowed mask, select_fallback_rq() can end up migrating a task
which is bound to a !active but online cpu to an active cpu. This is
dangerous because active is cleared before CPU_DOWN_PREPARE is called
and subsystems expect affinities of kthreads and other tasks to be
maintained till their CPU_DOWN_PREPARE callbacks are complete.

Consult cpu_online_mask instead.

Signed-off-by: Tejun Heo <tj(a)kernel.org>
Cc: Peter Zijlstra <peterz(a)infradead.org>
Cc: Ingo Molnar <mingo(a)elte.hu>
---
kernel/sched.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 3a8fb30..ca32adc 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2288,12 +2288,12 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu));

/* Look for allowed, online CPU in same node. */
- for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask)
+ for_each_cpu_and(dest_cpu, nodemask, cpu_online_mask)
if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))
return dest_cpu;

/* Any allowed, online CPU? */
- dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_active_mask);
+ dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);
if (dest_cpu < nr_cpu_ids)
return dest_cpu;

@@ -2302,6 +2302,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
rcu_read_lock();
cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
rcu_read_unlock();
+ /* breaking affinity, consider active mask instead */
dest_cpu = cpumask_any_and(cpu_active_mask, &p->cpus_allowed);

/*
--
1.6.4.2

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo(a)vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
 | 
Pages: 1
Prev: [PATCH 12/43] workqueue: merge feature parameters into flags
Next: [PATCH 09/43] acpi: use queue_work_on() instead of binding workqueue worker to cpu0