From fad156c2af227f42ca796cbb20ddc354a6dd9932 Mon Sep 17 00:00:00 2001 From: Usama Arif Date: Tue, 16 Jun 2026 07:15:18 -0700 Subject: block: invalidate cached plug timestamp after task switch 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 Link: https://patch.msgid.link/20260616141604.328820-3-usama.arif@linux.dev Signed-off-by: Jens Axboe --- include/linux/blkdev.h | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) (limited to 'include/linux/blkdev.h') diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 5070851cf924..9213a5716f95 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1222,16 +1222,12 @@ static inline void blk_flush_plug(struct blk_plug *plug, bool async) __blk_flush_plug(plug, async); } -/* - * tsk == current here - */ -static inline void blk_plug_invalidate_ts(struct task_struct *tsk) +static __always_inline void blk_plug_invalidate_ts(void) { - struct blk_plug *plug = tsk->plug; - - if (plug) - plug->cur_ktime = 0; - current->flags &= ~PF_BLOCK_TS; + if (unlikely(current->flags & PF_BLOCK_TS)) { + current->plug->cur_ktime = 0; + current->flags &= ~PF_BLOCK_TS; + } } int blkdev_issue_flush(struct block_device *bdev); @@ -1257,7 +1253,7 @@ static inline void blk_flush_plug(struct blk_plug *plug, bool async) { } -static inline void blk_plug_invalidate_ts(struct task_struct *tsk) +static inline void blk_plug_invalidate_ts(void) { } -- cgit v1.2.3