diff options
| author | Schspa Shi <schspa@gmail.com> | 2022-08-29 01:03:02 +0800 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-04-21 13:24:21 +0200 |
| commit | feffe5bb274dd3442080ef0e4053746091878799 (patch) | |
| tree | 0e69d00d399b44cc97094d2828d993fe6282fe22 /kernel/sched/rt.c | |
| parent | 223baf9d17f25e2608dbdff7232c095c1e612268 (diff) | |
sched/rt: Fix bad task migration for rt tasks
Commit 95158a89dd50 ("sched,rt: Use the full cpumask for balancing")
allows find_lock_lowest_rq() to pick a task with migration disabled.
The purpose of the commit is to push the current running task on the
CPU that has the migrate_disable() task away.
However, there is a race which allows a migrate_disable() task to be
migrated. Consider:
CPU0 CPU1
push_rt_task
check is_migration_disabled(next_task)
task not running and
migration_disabled == 0
find_lock_lowest_rq(next_task, rq);
_double_lock_balance(this_rq, busiest);
raw_spin_rq_unlock(this_rq);
double_rq_lock(this_rq, busiest);
<<wait for busiest rq>>
<wakeup>
task become running
migrate_disable();
<context out>
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, lowest_rq->cpu);
WARN_ON_ONCE(is_migration_disabled(p));
Fixes: 95158a89dd50 ("sched,rt: Use the full cpumask for balancing")
Signed-off-by: Schspa Shi <schspa@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Dwaine Gonyier <dgonyier@redhat.com>
Diffstat (limited to 'kernel/sched/rt.c')
| -rw-r--r-- | kernel/sched/rt.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 9d67dfbf1000..00e0e5074115 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2000,11 +2000,15 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq) * the mean time, task could have * migrated already or had its affinity changed. * Also make sure that it wasn't scheduled on its rq. + * It is possible the task was scheduled, set + * "migrate_disabled" and then got preempted, so we must + * check the task migration disable flag here too. */ if (unlikely(task_rq(task) != rq || !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_mask) || task_on_cpu(rq, task) || !rt_task(task) || + is_migration_disabled(task) || !task_on_rq_queued(task))) { double_unlock_balance(rq, lowest_rq); |