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Subject[PATCH RT 7/8] sched: migrate_enable: Use select_fallback_rq()
Date
migrate_enable() currently open-codes a variant of select_fallback_rq().
However, it does not have the "No more Mr. Nice Guy" fallback and thus
it will pass an invalid CPU to the migration thread if cpus_mask only
contains a CPU that is !active.

Signed-off-by: Scott Wood <swood@redhat.com>
---
This scenario will be more likely after the next patch, since
the migrate_disable_update check goes away. However, it could happen
anyway if cpus_mask was updated to a CPU other than the one we were
pinned to, and that CPU subsequently became inactive.
---
kernel/sched/core.c | 25 ++++++++++---------------
1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index eb27a9bf70d7..3a2d8251a30c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7368,6 +7368,7 @@ void migrate_enable(void)
if (p->migrate_disable_update) {
struct rq *rq;
struct rq_flags rf;
+ int cpu = task_cpu(p);

rq = task_rq_lock(p, &rf);
update_rq_clock(rq);
@@ -7377,21 +7378,15 @@ void migrate_enable(void)

p->migrate_disable_update = 0;

- WARN_ON(smp_processor_id() != task_cpu(p));
- if (!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
- const struct cpumask *cpu_valid_mask = cpu_active_mask;
- struct migration_arg arg;
- unsigned int dest_cpu;
-
- if (p->flags & PF_KTHREAD) {
- /*
- * Kernel threads are allowed on online && !active CPUs
- */
- cpu_valid_mask = cpu_online_mask;
- }
- dest_cpu = cpumask_any_and(cpu_valid_mask, &p->cpus_mask);
- arg.task = p;
- arg.dest_cpu = dest_cpu;
+ WARN_ON(smp_processor_id() != cpu);
+ if (!cpumask_test_cpu(cpu, &p->cpus_mask)) {
+ struct migration_arg arg = { p };
+ struct rq_flags rf;
+
+ rq = task_rq_lock(p, &rf);
+ update_rq_clock(rq);
+ arg.dest_cpu = select_fallback_rq(cpu, p);
+ task_rq_unlock(rq, p, &rf);

unpin_current_cpu();
preempt_lazy_enable();
--
1.8.3.1
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