From nobody Wed Nov 27 04:30:06 2024 Received: from mail-pf1-f173.google.com (mail-pf1-f173.google.com [209.85.210.173]) (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 1F4EE15689A for ; Mon, 14 Oct 2024 09:32:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.173 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728898371; cv=none; b=qVCrHZqdDZK3fSXExLSThS+NI/2ntia4ueYJhkOWGWvA0UemXMFGXq3Tc6/0JQhLq2KvYr+Vwngw5aUimnpPOapS8SZ1yFONLT9XTpaLdUbovXH/IzhR9UlK6MZbpi+wa2SCI66NYxoFvMXAgSODl4v9G0GN1sErPEY4TtSWH6g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728898371; c=relaxed/simple; bh=KPYlAEycxQewUTOUahfTRncxoD2+pw617t+q4Tal4uA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=HUCYC83ZzyRD8BZQZiddhhxAoR4nKJ1wvIrd1pnQORvTQWztCY2kcnFAkU/N8aOZRvq1Sc5olvI0KP89fm70vU18MURL8ahGzDO1/k8wgQtXLuFTwKy0aHINM6UYU5XYgZwWsf9YJMd6T/pi59C/SOam+jxy0tHTxy8tWzr7Sbs= 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=SXF2Ncj6; arc=none smtp.client-ip=209.85.210.173 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="SXF2Ncj6" Received: by mail-pf1-f173.google.com with SMTP id d2e1a72fcca58-71e5130832aso942366b3a.0 for ; Mon, 14 Oct 2024 02:32:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1728898369; x=1729503169; 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=SXF2Ncj6g9TFV6T6I8WCm2zJGEIq+Ktc6KmjRAaO4i+Dy2SycqoTEvA5UHe48HApJk PRfzmOOuh6JgxPY0cjsuIVz/svvHGnxtTzM2UtlZrCvAzy0Z5uRjc7vuYAUnLnEuuO+r gMwNSKF5e55VGPoaV1mn2TUM3TPP7YMG31R/A3YJdayhJVoLPlZCnBgRmo+ThN2MOuPo pXxFIVR0C5RidkPJs+8eoF3WoARlNUQS2PLg8AQ7zJ2Nes/qmVPV9u1hXmmw3pHjSxsD jDQlVInhtoUuPyQnznQipG/rrImp+WUy1Bonyu+SxQwr3Z0p8rFYNiKUXxzoCzu1ATtX onlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1728898369; x=1729503169; 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=d2rPFe0r4laYcTqBMkkJ7NQyr52+vJ5yAnODzIGmZ6wWdebKBtFLGpeBShGbQZ8yDZ 2zG2xkfYXJmaduuv+Pm++51hP9sHSL8Hdob+85wOoNzMHgl2TIEeyIJEp4HlMLZcdL12 xD9M92BKB3fuZTkpUglkqVnFZhXc3kNDpYzC6eldjPLoY+5VNPXeXvmBR8iDqwPZ7/lM BPQwTaEVBZBmH+FFAVHAOgyS+8pw0XA0XnhMiKg9pkc/txYR9VLgFEx2gQE2x326TdUE +JsGePQ8ySmCCLxaUjuYI+4pe73v8Vf8vhI+0QdE6om5G+ghwRPS3pgOWwX9lOnVhUiw m7OQ== X-Forwarded-Encrypted: i=1; AJvYcCVuGF2htuq3WT8nM5/wE0xTQWJb6rOAi1g4cJE4wEF5Shs9rVUN8wlpCip1oD0C/4JvQuHGAsNi9aLYh34=@vger.kernel.org X-Gm-Message-State: AOJu0Yz6ADRbXVsu2O70ZQSaC9l8kPX51bkjdN71T69OWImH2+KlyDMv 8DATLDKAVKXMU3iNiYVa/ADytxmzxotAmnGPeYuwavGT0DXuvPNPhttMY99hAhc= X-Google-Smtp-Source: AGHT+IGBMDRNMKLO//5sYGfMXInq4aAF8gwrpnqlC4y4fsMFrWqYiR5I8wa6nev+Irqz/anUVaW0UQ== X-Received: by 2002:a05:6a00:23d1:b0:71e:3b51:e856 with SMTP id d2e1a72fcca58-71e4c13dd24mr10888349b3a.1.1728898369262; Mon, 14 Oct 2024 02:32:49 -0700 (PDT) Received: from PXLDJ45XCM.bytedance.net ([61.213.176.11]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-71e60bbec80sm2339338b3a.95.2024.10.14.02.32.44 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 14 Oct 2024 02:32:48 -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 RESEND v3 2/3] block: fix ordering between checking QUEUE_FLAG_QUIESCED and adding requests Date: Mon, 14 Oct 2024 17:29:33 +0800 Message-Id: <20241014092934.53630-3-songmuchun@bytedance.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20241014092934.53630-1-songmuchun@bytedance.com> References: <20241014092934.53630-1-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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); =20 +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 =3D !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) =20 might_sleep_if(!async && hctx->flags & BLK_MQ_F_BLOCKING); =20 - /* - * 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 =3D !blk_queue_quiesced(hctx->queue) && - blk_mq_hctx_has_pending(hctx)); + need_run =3D blk_mq_hw_queue_need_run(hctx); + if (!need_run) { + unsigned long flags; =20 - 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 =3D blk_mq_hw_queue_need_run(hctx); + spin_unlock_irqrestore(&hctx->queue->queue_lock, flags); + + if (!need_run) + return; + } =20 if (async || !cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) { blk_mq_delay_run_hw_queue(hctx, 0); --=20 2.20.1