From patchwork Sat Sep 14 07:28:43 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muchun Song X-Patchwork-Id: 13804301 Received: from mail-pf1-f170.google.com (mail-pf1-f170.google.com [209.85.210.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EF5F219D098 for ; Sat, 14 Sep 2024 07:30:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.170 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726299060; cv=none; b=GCqwi8ufPcOXGl/bbbO76rj8hmHBGARlX5gWjREqMXAUtfEPijVYzDHfcChGUBbtMWM9d0De81fXK+358/hCP05fo0dI8zgZTpwk8zzfBacsKD/vkQGEM08tmb6Afgns4Id4R/ORM5GHZm61fVnPipHs+HQ1+JYeB6L1v2DMXQU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726299060; c=relaxed/simple; bh=KPYlAEycxQewUTOUahfTRncxoD2+pw617t+q4Tal4uA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=VrF2KBz1yFYgsIPvDNMSdE2wa3xGUKz1w/sj8DArxOZ1JKj/ShTeJdVIczemcBqKU7vKsjlGye7Oz73OcEri9gB1DefZowQ9j8vNsZiuOLavQn0GNpSewC9Gussj/71J1Pgb5WY0rtB4XA32JAlzrPbpkhktQaHFfXIQIa1KUzo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com; spf=pass smtp.mailfrom=bytedance.com; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b=ROPYQzDg; arc=none smtp.client-ip=209.85.210.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=bytedance.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bytedance.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bytedance.com header.i=@bytedance.com header.b="ROPYQzDg" Received: by mail-pf1-f170.google.com with SMTP id d2e1a72fcca58-718d606726cso1911303b3a.3 for ; Sat, 14 Sep 2024 00:30:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1726299058; x=1726903858; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=08ooLorU1l3a5zJ7wHu/dTOBgAYH9XEx3vZXzuZBYRU=; b=ROPYQzDgQr5oHOSBnoXaq9/UzDSftmVWVuR6JKwj/zXA8dYrTapQHCRtGHuEeNYDCt /16zmyOk7fI/NEUcQHshR4U7SXRm2k/JsSMDzWpIeHNufqCNBnhTJPz2XV3C9rfIDGKw I0zcQhZ6rn9hqsLagME57Rg/YdxKvKemarvP4kDNl9dlAucB/lrYiosoSkPnfMY2Ye8C ZYT6mF96xIc6/bXkMHdMAyM5yiRyXunOGjJSzhtkfkiC6stnZ5H6HoRXU0j289/XgSsh szVUY2GnW8B5IpZWjmtmQiQWU2Ysya1w6Bvh/D3hL1gNFK40iBI8FivEikDrC1OlkTBM fziw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1726299058; x=1726903858; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=08ooLorU1l3a5zJ7wHu/dTOBgAYH9XEx3vZXzuZBYRU=; b=IW/1nxX8WlcWXkIr4yqaCyyJG1sHN3/oov8tqq+El0n0/7LV7ZrpR+1mublTLu+gOD KuOLfshewxU8/NionyIVWCEii3+O78fi+8DUQbobCBFPC4jlP7JLJOmN/1NgxMjq01ip 8pJ0+jyjyyTHtThxB3gQKiagHdZdD0hb3TiTRluOXCGqGns14ZjI9MUUQKScpob8XLiM WTcetsRhoDTaq1Y+A+jH97ah2BotHnw2GYmG1xrTj/4Ma10nFGW5qUzGslIkC+I6MeYs VMPnCsFP68+Io2sedmhQp8rwIoVNKAJ+5yoZRAvuTIepMfAiaJJMpxz741JUIoDwfhfl z+yw== X-Gm-Message-State: AOJu0YyXBbScbGUiEdS+9AyOxGFgKz/ILgy91cIWkqsMeQ2CDB60Zatd eR1dEYnBNVHNR0ttv6apXyXq2PRIGRD8ife34tRMmAM9GEp4GvNcOHSkLV7gekY= X-Google-Smtp-Source: AGHT+IGZG9wrGWEYM7ouukqw6bRDRDCHTs/ZJP2/izZHnuPe05qp1RIBdiw0AkIVpTS2FuGBrP35Tg== X-Received: by 2002:a05:6a00:1883:b0:706:58ef:613 with SMTP id d2e1a72fcca58-719262066efmr13431606b3a.27.1726299058203; Sat, 14 Sep 2024 00:30:58 -0700 (PDT) Received: from PXLDJ45XCM.bytedance.net ([61.213.176.6]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-71944b9ac05sm555687b3a.155.2024.09.14.00.30.55 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 14 Sep 2024 00:30:57 -0700 (PDT) From: Muchun Song To: axboe@kernel.dk, ming.lei@redhat.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev, Muchun Song , stable@vger.kernel.org Subject: [PATCH v3 2/3] block: fix ordering between checking QUEUE_FLAG_QUIESCED and adding requests Date: Sat, 14 Sep 2024 15:28:43 +0800 Message-Id: <20240914072844.18150-3-songmuchun@bytedance.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20240914072844.18150-1-songmuchun@bytedance.com> References: <20240914072844.18150-1-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Supposing the following scenario. CPU0 CPU1 blk_mq_insert_request() 1) store blk_mq_unquiesce_queue() blk_queue_flag_clear() 3) store blk_mq_run_hw_queues() blk_mq_run_hw_queue() if (!blk_mq_hctx_has_pending()) 4) load return blk_mq_run_hw_queue() if (blk_queue_quiesced()) 2) load return blk_mq_sched_dispatch_requests() The full memory barrier should be inserted between 1) and 2), as well as between 3) and 4) to make sure that either CPU0 sees QUEUE_FLAG_QUIESCED is cleared or CPU1 sees dispatch list or setting of bitmap of software queue. Otherwise, either CPU will not rerun the hardware queue causing starvation. So the first solution is to 1) add a pair of memory barrier to fix the problem, another solution is to 2) use hctx->queue->queue_lock to synchronize QUEUE_FLAG_QUIESCED. Here, we chose 2) to fix it since memory barrier is not easy to be maintained. Fixes: f4560ffe8cec ("blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue") Cc: stable@vger.kernel.org Cc: Muchun Song Signed-off-by: Muchun Song Reviewed-by: Ming Lei --- block/blk-mq.c | 47 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 34 insertions(+), 13 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index b2d0f22de0c7f..ff6df6c7eeb25 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2202,6 +2202,24 @@ void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs) } EXPORT_SYMBOL(blk_mq_delay_run_hw_queue); +static inline bool blk_mq_hw_queue_need_run(struct blk_mq_hw_ctx *hctx) +{ + bool need_run; + + /* + * When queue is quiesced, we may be switching io scheduler, or + * updating nr_hw_queues, or other things, and we can't run queue + * any more, even blk_mq_hctx_has_pending() can't be called safely. + * + * And queue will be rerun in blk_mq_unquiesce_queue() if it is + * quiesced. + */ + __blk_mq_run_dispatch_ops(hctx->queue, false, + need_run = !blk_queue_quiesced(hctx->queue) && + blk_mq_hctx_has_pending(hctx)); + return need_run; +} + /** * blk_mq_run_hw_queue - Start to run a hardware queue. * @hctx: Pointer to the hardware queue to run. @@ -2222,20 +2240,23 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) might_sleep_if(!async && hctx->flags & BLK_MQ_F_BLOCKING); - /* - * When queue is quiesced, we may be switching io scheduler, or - * updating nr_hw_queues, or other things, and we can't run queue - * any more, even __blk_mq_hctx_has_pending() can't be called safely. - * - * And queue will be rerun in blk_mq_unquiesce_queue() if it is - * quiesced. - */ - __blk_mq_run_dispatch_ops(hctx->queue, false, - need_run = !blk_queue_quiesced(hctx->queue) && - blk_mq_hctx_has_pending(hctx)); + need_run = blk_mq_hw_queue_need_run(hctx); + if (!need_run) { + unsigned long flags; - if (!need_run) - return; + /* + * Synchronize with blk_mq_unquiesce_queue(), because we check + * if hw queue is quiesced locklessly above, we need the use + * ->queue_lock to make sure we see the up-to-date status to + * not miss rerunning the hw queue. + */ + spin_lock_irqsave(&hctx->queue->queue_lock, flags); + need_run = blk_mq_hw_queue_need_run(hctx); + spin_unlock_irqrestore(&hctx->queue->queue_lock, flags); + + if (!need_run) + return; + } if (async || !cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) { blk_mq_delay_run_hw_queue(hctx, 0);