blk_time_get_ns() caches ktime_get_ns() in current->plug->cur_ktime and marks the task with PF_BLOCK_TS. That cache is only valid while the task keeps running; if the task is switched out, wall-clock time advances and the cached value must not be reused when the task runs again. The existing invalidation covers explicit plug flushes through __blk_flush_plug(), and the schedule() / rtmutex paths through sched_update_worker(). It does not cover in-kernel preemption paths such as preempt_schedule(), preempt_schedule_notrace(), and preempt_schedule_irq(), which enter __schedule(SM_PREEMPT) directly and return without calling sched_update_worker(). As a result, a task preempted while holding a plug with PF_BLOCK_TS set can reuse a stale plug->cur_ktime after it is scheduled back in. blk-iocost then consumes that stale timestamp through ioc_now(), producing stale vnow values for throttle decisions, and through ioc_rqos_done(), inflating on-queue time and feeding false missed-QoS samples into vrate adjustment. Move the schedule-side invalidation to finish_task_switch(), which runs for the scheduled-in task after every actual context switch regardless of which schedule entry point was used. Keep __blk_flush_plug() as the explicit flush/finish-plug invalidation path, and remove only the PF_BLOCK_TS handling from sched_update_worker(). Fixes: 06b23f92af87 ("block: update cached timestamp post schedule/preemption") Cc: stable@vger.kernel.org Signed-off-by: Usama Arif --- kernel/sched/core.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8b791e9e9f67..bf024ca115ff 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5368,6 +5368,13 @@ static struct rq *finish_task_switch(struct task_struct *prev) */ kmap_local_sched_in(); + /* + * Any cached block-layer timestamp (plug->cur_ktime) is stale now, + * invalidate it. + */ + if (unlikely(current->flags & PF_BLOCK_TS)) + blk_plug_invalidate_ts(current); + fire_sched_in_preempt_notifiers(current); /* * When switching through a kernel thread, the loop in @@ -7290,12 +7297,10 @@ static inline void sched_submit_work(struct task_struct *tsk) static void sched_update_worker(struct task_struct *tsk) { - if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER | PF_BLOCK_TS)) { - if (tsk->flags & PF_BLOCK_TS) - blk_plug_invalidate_ts(tsk); + if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) { if (tsk->flags & PF_WQ_WORKER) wq_worker_running(tsk); - else if (tsk->flags & PF_IO_WORKER) + else io_wq_worker_running(tsk); } } -- 2.53.0-Meta