hulk inclusion category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13564 CVE: NA ---------------------------------------- Consider the following sequence on a CPU configured with nohz_full: 1) A task P runs in cgroup A, and cgroup A becomes throttled due to CFS bandwidth control. The gse (cgroup A) where the task P attached is dequeued and the CPU switches to idle. 2) Before cgroup A is unthrottled, task P is migrated from cgroup A to another cgroup B (not throttled). During sched_move_task(), the task P is observed as queued but not running, and therefore no resched_curr() is triggered. 3) Since the CPU is nohz_full, it remains in do_idle() waiting for an explicit scheduling event, i.e., resched_curr(). 4) For kernel <= 5.10: Later, cgroup A is unthrottled. However, the task P has already been migrated out of cgroup A, so unthrottle_cfs_rq() may observe load_weight == 0 and return early without resched_curr() called. For kernel >= 6.6: The unthrottling path normally triggers `resched_curr()` almost cases even when no runnable tasks remain in the unthrottled cgroup, preventing the idle stall described above. However, if cgroup A is removed before it gets unthrottled, the unthrottling path for cgroup A is never executed. In a result, no `resched_curr()` can be called. 5) At this point, the task P is runnable in cgroup B (not throttled), but the CPU remains in do_idle() with no pending reschedule point. The system stays in this state until an unrelated event (e.g. a new task wakeup or any cases) that can trigger a resched_curr() breaks the nohz_full idle state, and then the task P finally gets scheduled. The root cause is that sched_move_task() may classify the task as only queued, not running, and therefore fails to trigger a resched_curr(), while the later unthrottling path no longer has visibility of the migrated task. Preserve the existing behavior for running tasks by issuing resched_curr(), and explicitly invoke check_preempt_curr() for tasks that were queued at the time of migration. This ensures that runnable tasks are reconsidered for scheduling even when nohz_full suppresses periodic ticks. Fixes: 29f59db3a74b ("sched: group-scheduler core") Signed-off-by: Zicheng Qu <quzicheng@huawei.com> --- kernel/sched/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 765e437732be..9c4e280fb56f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6563,8 +6563,10 @@ void sched_move_task(struct task_struct *tsk) sched_change_group(tsk, TASK_MOVE_GROUP); - if (queued) + if (queued) { enqueue_task(rq, tsk, queue_flags); + check_preempt_curr(rq, tsk, 0); + } if (running) { set_curr_task(rq, tsk); /* -- 2.34.1