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| author | Schspa Shi <schspa@gmail.com> | 2022-08-28 20:03:02 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2023-05-11 17:03:32 +0300 |
| commit | 6472a6d0c79826256bfa3a6b45710dd499a984bf (patch) | |
| tree | 53d961442a7512f325e13af0554440f755e11dc2 /kernel/sched | |
| parent | 1969b143d09658e2e096e2252fcd594c8f8647b6 (diff) | |
| download | linux-6472a6d0c79826256bfa3a6b45710dd499a984bf.tar.xz | |
sched/rt: Fix bad task migration for rt tasks
[ Upstream commit feffe5bb274dd3442080ef0e4053746091878799 ]
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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/deadline.c | 1 | ||||
| -rw-r--r-- | kernel/sched/rt.c | 4 |
2 files changed, 5 insertions, 0 deletions
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 9ae8f41e3372..f7d381b6c313 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2246,6 +2246,7 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq) !cpumask_test_cpu(later_rq->cpu, &task->cpus_mask) || task_on_cpu(rq, task) || !dl_task(task) || + is_migration_disabled(task) || !task_on_rq_queued(task))) { double_unlock_balance(rq, later_rq); later_rq = NULL; diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 0a11f44adee5..4f5796dd26a5 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); |