From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DFCA43CF032 for ; Thu, 11 Jun 2026 23:15:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781219714; cv=none; b=XzBPIJmG9f9JnUCgl9urRIOQm1QR/wdyVR4sG8oLz6Fh45i2RSQAzKgg35SPrmDjn4ceXlNDM3EWio97ofbhWYTBwEeYsOaEyruOcj087twqTgUaWo66VwsIsgR4hUBERYEHKprdXJTJWBz1qjcX34hkDBqpNygecyHrRfY6/Vg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781219714; c=relaxed/simple; bh=QD69d2OJHwOtuSaX+DoKywFbAEQo0UEq/e3/Fn2QjUI=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=JWGiLayTpo9yZdX+Z4VolBAa67wOZDrlmEOx9nsYb22uix2BMV3xcW0KB2Rndc49ParMVgRAhZgXrU4ypIyNSIzGdSGSf1ZRzr0Y4ZdV2W9gzfNpSvJv9WghU17NBBBsjaWRAr82R5+FnlF6kGP7dzBVnTWmnTQYCXmJ9zE7GjU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=NVtko3so; arc=none smtp.client-ip=95.215.58.188 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="NVtko3so" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781219700; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=ShBjYPEYExajE8ngaKwJEtPoM9APFzTLlxCb37S7wzg=; b=NVtko3soc9++gRfLlIoaBBOFQi0d+fACKKMTE/tCvKwXnD6KettXDw90iH4kYyHTlloMkV Dq3bDtenVXhDxGVOo+guXKNmUzUGkxUOvAeeu0ETMVdZyBdZ6TA1UHu4fh05hjy/Y0/hFO sif6VgxrLQBckRWUx1Jvkn7itQFCQCI= From: Usama Arif To: axboe@kernel.dk, linux-block@vger.kernel.org, bsegall@google.com, dietmar.eggemann@arm.com, juri.lelli@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org, mgorman@suse.de, mingo@redhat.com, peterz@infradead.org, rostedt@goodmis.org, vincent.guittot@linaro.org, vschneid@redhat.com Cc: shakeel.butt@linux.dev, hannes@cmpxchg.org, riel@surriel.com, kernel-team@meta.com, Usama Arif , stable@vger.kernel.org Subject: [PATCH] block: invalidate cached plug timestamp after task switch Date: Thu, 11 Jun 2026 16:14:28 -0700 Message-ID: <20260611231428.345098-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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