From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta1.migadu.com (out-171.mta1.migadu.com [95.215.58.171]) (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 13DDD397329 for ; Fri, 12 Jun 2026 09:41:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781257269; cv=none; b=GxijXmZOzzksURYJj4YDJ4RBM/xD6p1xf/X1P2NOBEqkksca5YJiQOchKSqr60m/2rOAF7gC0mR+IV4i/5ZrgYbhnw5V1VSjIlfu8I+K6tvdCyuNtmN14C8e+TNFW293/EPOc5ktgAnCnFdnk/tSpRhYzmLyGiAd+ag5hmWKlvg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781257269; c=relaxed/simple; bh=RdtnOaQ/45dYn/VGBVrYYUdalAsIkR0FBWEJgJ/G6PA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=OGKa/z3Dd1JmHq9gSrTuuThBzCKFEAhSBmeP41yiMHrraz6m9APJ81cuR+2aQPEOhk/CP1VzpN+sH+vZH2wOGgseSuK28ajIy/PpPVAyg8K1pmRVUalJq8d6D4G8khwDDy+twwseSqoRY2dwot50WfZPjqVuncXpvD+UrONoL7g= 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=hRZ7YAGr; arc=none smtp.client-ip=95.215.58.171 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="hRZ7YAGr" 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=1781257253; 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=bw1xWLPB0CZgS93U9XBxSKNhegqUQ0O3PEyPxeYXm5M=; b=hRZ7YAGr1p84LtrvGgfOgrRKgPfQfKkMR3+8HJUZIvIReXEvJ/9W3TkLHsHIyyi4ddUIL4 SqMaysNj+BsyDcIOuGmTnSnqOBQn1ryR2y0gDgeZft/lK+uHsN83KUvUNKqWPa8FAQ8KrS JdFj/BeP5avW7NREx86ZgvsVE9kM4TQ= 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 v2] block: invalidate cached plug timestamp after task switch Date: Fri, 12 Jun 2026 02:40:42 -0700 Message-ID: <20260612094042.3350401-1-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 --- v1 -> v2: https://lore.kernel.org/all/20260611231428.345098-1-usama.arif@linux.dev/ - Make the function just blk_plug_invalidate_ts(), move the check for PF_BLOCK_TS flag into blk_plug_invalidate_ts and make it __always_inline (Peter Zijlstra). --- include/linux/blkdev.h | 17 ++++++++--------- kernel/sched/core.c | 12 ++++++++---- 2 files changed, 16 insertions(+), 13 deletions(-) diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 57e84d59a642..1c1fd31ce187 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1216,16 +1216,15 @@ 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 (unlikely(current->flags & PF_BLOCK_TS)) { + struct blk_plug *plug = current->plug; - if (plug) - plug->cur_ktime = 0; - current->flags &= ~PF_BLOCK_TS; + if (plug) + plug->cur_ktime = 0; + current->flags &= ~PF_BLOCK_TS; + } } int blkdev_issue_flush(struct block_device *bdev); @@ -1251,7 +1250,7 @@ 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) { } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8b791e9e9f67..e97e98c33be5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5368,6 +5368,12 @@ 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. + */ + blk_plug_invalidate_ts(); + fire_sched_in_preempt_notifiers(current); /* * When switching through a kernel thread, the loop in @@ -7290,12 +7296,10 @@ 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