From patchwork Tue Sep 3 08:16:53 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Muchun Song X-Patchwork-Id: 13788250 Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (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 229C021C176 for ; Tue, 3 Sep 2024 08:17:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.179 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725351442; cv=none; b=IejYYrUgYw2vTMiUe06g+VPjy+xXHCjEYfybqxVCjzxAL6r2l1Hsk9MCpIZEQptySHWY+3T17rTXfMeAZQzHSvyIf+/VX/QMJDRIqfKC7mr/zB4yMLgMjn+5pp3wF+wk2g5LiyoLPLswOT4PPjdLrDmUL8RB1MtTq514yWo/3Q8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725351442; c=relaxed/simple; bh=2nS7H6L6WID7zbgTfR3cXsYRR840ppC8iAY3XsHIAg0=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pIVhetcdvJ5Pvphg2fIl8M3EcbLvJHuMO/1kKZ5JdEsYrOiysMhJ1U2fpHYOtxXi/w/s96kF7YVzSgskZOfaQA6K7h4ey1rJU73mo8pdNnBtmoWYTrm7a0CqOWUOJu95fMdzsOdCnBC5bfou5SaPnwIE3Mm//VsvBh/e1iUdlmQ= 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=eR1ma8vP; arc=none smtp.client-ip=209.85.214.179 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="eR1ma8vP" Received: by mail-pl1-f179.google.com with SMTP id d9443c01a7336-1fee6435a34so34903575ad.0 for ; Tue, 03 Sep 2024 01:17:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1725351440; x=1725956240; 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=zDpBNlTp4IAb2nYSzA4S5C3FeNDLg/TiXjgWPP/Ofy0=; b=eR1ma8vP1rVo2mTTdEb7mmcigU/DSrA3KFc1Tano8EYDkLPVUG2vguMd6M3o61aaUd zGUUv0JzlEQLNTQu3rIsFF3+ER1OscK1lRxPtcWtbmnfwrTyl4uVEnryl2qxSnSOTIKO kSbNuWgU14s7AgajBYideY69lEMcARo54QaeNv9KmQ7gcK2XKEB+1Xn3nXtHJ6X75lhK Yb9HFl8gafzsGH5BQDQaV9Uub1dqjn8fx/RorIkcAytnoPbeoCzLTVUIHIL6QvuVMe/g 8Pg+MlhNbZ93OJlPLsHcjKMiceZC8E5VnEvxVcsigBKaqULh/oeHtpjsHQOavcqrAL19 phyQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1725351440; x=1725956240; 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=zDpBNlTp4IAb2nYSzA4S5C3FeNDLg/TiXjgWPP/Ofy0=; b=nZrDzkxu/t2Gk+v7l6lu5KxMkQMK5Cd5sfhQiXGz2IHe3+FA+y1P62LrdLog4ScKpu 07UtboVJ0Gz9Z8w++PLI20eSAe0XOq8RZLKGbLOuGVAUXXMSX+4vfsIzfxS+nOdDwOfX lriwUVSReeL1FHHVwzQ/X6W4d4BCHQ3eyOm2VBIEut790ZiVaiMhruvLmtfOgNEh90Qq K2f76hVgZGuLpwnxZfbdx5crdiWxpb08A2p2JmTcLTzxNPjLvGjxjusvPxRdnhBR3fwo WAF0677LoDVoXZCDR8UMUvFRXgieeAGou0RBcuaAgCF2O6VGyN9tBc0I82QKBSZAPBFL /rbQ== X-Gm-Message-State: AOJu0YxsRklNFhGP/YiJzJj6ylqjLTcFF5pubpnPUfT+W2Oa72dA5Y/r t+ciprnF+7ZkxdYhk1qrWoseU2ZRQzCp8O1CQrFuTcb8MQd1elBWL9VQvPbRmqA= X-Google-Smtp-Source: AGHT+IGlXjkmm4wRivHlKxkzFWkFVKdYxcu00qrJi9p0aoh/oPB1y4lwMJCCvMAwLqQVPKWe0Wg4uw== X-Received: by 2002:a17:903:230a:b0:203:a13a:c49e with SMTP id d9443c01a7336-20699acb7bfmr12843815ad.1.1725351440502; Tue, 03 Sep 2024 01:17:20 -0700 (PDT) Received: from PXLDJ45XCM.bytedance.net ([139.177.225.235]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-20559cae667sm38155435ad.95.2024.09.03.01.17.16 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 03 Sep 2024 01:17:19 -0700 (PDT) From: Muchun Song To: axboe@kernel.dk, ming.lei@redhat.com, yukuai1@huaweicloud.com Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, muchun.song@linux.dev, Muchun Song , stable@vger.kernel.org Subject: [PATCH v2 3/3] block: fix ordering between checking BLK_MQ_S_STOPPED and adding requests Date: Tue, 3 Sep 2024 16:16:53 +0800 Message-Id: <20240903081653.65613-4-songmuchun@bytedance.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20240903081653.65613-1-songmuchun@bytedance.com> References: <20240903081653.65613-1-songmuchun@bytedance.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Supposing first scenario with a virtio_blk driver. CPU0 CPU1 blk_mq_try_issue_directly() __blk_mq_issue_directly() q->mq_ops->queue_rq() virtio_queue_rq() blk_mq_stop_hw_queue() virtblk_done() blk_mq_request_bypass_insert() blk_mq_start_stopped_hw_queues() /* Add IO request to dispatch list */ 1) store blk_mq_start_stopped_hw_queue() clear_bit(BLK_MQ_S_STOPPED) 3) store blk_mq_run_hw_queue() blk_mq_run_hw_queue() if (!blk_mq_hctx_has_pending()) if (!blk_mq_hctx_has_pending()) 4) load return return blk_mq_sched_dispatch_requests() blk_mq_sched_dispatch_requests() if (blk_mq_hctx_stopped()) 2) load if (blk_mq_hctx_stopped()) return return __blk_mq_sched_dispatch_requests() __blk_mq_sched_dispatch_requests() Supposing another scenario. CPU0 CPU1 blk_mq_requeue_work() /* Add IO request to dispatch list */ 1) store virtblk_done() blk_mq_run_hw_queues()/blk_mq_delay_run_hw_queues() blk_mq_start_stopped_hw_queues() if (blk_mq_hctx_stopped()) 2) load blk_mq_start_stopped_hw_queue() continue clear_bit(BLK_MQ_S_STOPPED) 3) store blk_mq_run_hw_queue()/blk_mq_delay_run_hw_queue() blk_mq_run_hw_queue() if (!blk_mq_hctx_has_pending()) 4) load return blk_mq_sched_dispatch_requests() Both scenarios are similar, 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 BLK_MQ_S_STOPPED is cleared or CPU1 sees dispatch list. Otherwise, either CPU will not rerun the hardware queue causing starvation of the request. The easy way to fix it is to add the essential full memory barrier into helper of blk_mq_hctx_stopped(). In order to not affect the fast path (hardware queue is not stopped most of the time), we only insert the barrier into the slow path. Actually, only slow path needs to care about missing of dispatching the request to the low-level device driver. Fixes: 320ae51feed5c ("blk-mq: new multi-queue block IO queueing mechanism") Cc: stable@vger.kernel.org Cc: Muchun Song Signed-off-by: Muchun Song Reviewed-by: Ming Lei --- block/blk-mq.c | 6 ++++++ block/blk-mq.h | 13 +++++++++++++ 2 files changed, 19 insertions(+) diff --git a/block/blk-mq.c b/block/blk-mq.c index ac39f2a346a52..48a6a437fba5e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2413,6 +2413,12 @@ void blk_mq_start_stopped_hw_queue(struct blk_mq_hw_ctx *hctx, bool async) return; clear_bit(BLK_MQ_S_STOPPED, &hctx->state); + /* + * Pairs with the smp_mb() in blk_mq_hctx_stopped() to order the + * clearing of BLK_MQ_S_STOPPED above and the checking of dispatch + * list in the subsequent routine. + */ + smp_mb__after_atomic(); blk_mq_run_hw_queue(hctx, async); } EXPORT_SYMBOL_GPL(blk_mq_start_stopped_hw_queue); diff --git a/block/blk-mq.h b/block/blk-mq.h index 260beea8e332c..f36f3bff70d86 100644 --- a/block/blk-mq.h +++ b/block/blk-mq.h @@ -228,6 +228,19 @@ static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data static inline bool blk_mq_hctx_stopped(struct blk_mq_hw_ctx *hctx) { + /* Fast path: hardware queue is not stopped most of the time. */ + if (likely(!test_bit(BLK_MQ_S_STOPPED, &hctx->state))) + return false; + + /* + * This barrier is used to order adding of dispatch list before and + * the test of BLK_MQ_S_STOPPED below. Pairs with the memory barrier + * in blk_mq_start_stopped_hw_queue() so that dispatch code could + * either see BLK_MQ_S_STOPPED is cleared or dispatch list is not + * empty to avoid missing dispatching requests. + */ + smp_mb(); + return test_bit(BLK_MQ_S_STOPPED, &hctx->state); }