From patchwork Thu Jan 11 15:54:48 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ming Lei X-Patchwork-Id: 13517568 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 8532E4F898 for ; Thu, 11 Jan 2024 15:55:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MFuKJNg8" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704988500; 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=N2zkMhK+45qG/GcFjunTZZrztvgu3syuF871fW0x/3Y=; b=MFuKJNg85wraKXFTkfsE7kv1ZuckhuB+rXxXOEEnp7fbPtW4orZWrNQ5yQ8U48Cqa6lxrd VC7MIHTpe6NVXQbm3kKexJ/JXeAaAKZeJMsDqO+6RgJR7Mzu35DnHE7JBzprRdNQXL1uAp 7fwC/T/D8F0CQPfgo3TXoPgxDQ0g3Ok= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-649-S5zCa7FkNraoVV9QC4WrkQ-1; Thu, 11 Jan 2024 10:54:59 -0500 X-MC-Unique: S5zCa7FkNraoVV9QC4WrkQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 950671C106A3; Thu, 11 Jan 2024 15:54:58 +0000 (UTC) Received: from localhost (unknown [10.72.116.3]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0A2015012; Thu, 11 Jan 2024 15:54:56 +0000 (UTC) From: Ming Lei To: Jens Axboe , linux-block@vger.kernel.org Cc: David Jeffery , Gabriel Krisman Bertazi , Jan Kara , Kemeng Shi , Ming Lei , Changhui Zhong Subject: [PATCH] blk-mq: fix IO hang from sbitmap wakeup race Date: Thu, 11 Jan 2024 23:54:48 +0800 Message-ID: <20240111155448.4097173-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 In blk_mq_mark_tag_wait(), __add_wait_queue() may be re-ordered with the following blk_mq_get_driver_tag() in case of getting driver tag failure. Then in __sbitmap_queue_wake_up(), waitqueue_active() may not observe the added waiter in blk_mq_mark_tag_wait() and wake up nothing, meantime blk_mq_mark_tag_wait() can't get driver tag successfully. This issue can be reproduced by running the following test in loop, and fio hang can be observed in < 30min when running it on my test VM in laptop. modprobe -r scsi_debug modprobe scsi_debug delay=0 dev_size_mb=4096 max_queue=1 host_max_queue=1 submit_queues=4 dev=`ls -d /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/* | head -1 | xargs basename` fio --filename=/dev/"$dev" --direct=1 --rw=randrw --bs=4k --iodepth=1 \ --runtime=100 --numjobs=40 --time_based --name=test \ --ioengine=libaio Fix the issue by adding one explicit barrier in blk_mq_mark_tag_wait(), which is just fine in case of running out of tag. Apply the same pattern in blk_mq_get_tag() which should have same risk. Reported-by: Changhui Zhong Signed-off-by: Ming Lei --- BTW, Changhui is planning to upstream the test case to blktests. block/blk-mq-tag.c | 19 +++++++++++++++++++ block/blk-mq.c | 16 ++++++++++++++++ 2 files changed, 35 insertions(+) diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index cc57e2dd9a0b..29f77cae8eb2 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -179,6 +179,25 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) sbitmap_prepare_to_wait(bt, ws, &wait, TASK_UNINTERRUPTIBLE); + /* + * Add one explicit barrier since __blk_mq_get_tag() may not + * imply barrier in case of failure. + * + * Order adding us to wait queue and the following allocating + * tag in __blk_mq_get_tag(). + * + * The pair is the one implied in sbitmap_queue_wake_up() + * which orders clearing sbitmap tag bits and + * waitqueue_active() in __sbitmap_queue_wake_up(), since + * waitqueue_active() is lockless + * + * Otherwise, re-order of adding wait queue and getting tag + * may cause __sbitmap_queue_wake_up() to wake up nothing + * because the waitqueue_active() may not observe us in wait + * queue. + */ + smp_mb(); + tag = __blk_mq_get_tag(data, bt); if (tag != BLK_MQ_NO_TAG) break; diff --git a/block/blk-mq.c b/block/blk-mq.c index fb29ff5cc281..54545a4792bf 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1847,6 +1847,22 @@ static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx, wait->flags &= ~WQ_FLAG_EXCLUSIVE; __add_wait_queue(wq, wait); + /* + * Add one explicit barrier since blk_mq_get_driver_tag() may + * not imply barrier in case of failure. + * + * Order adding us to wait queue and allocating driver tag. + * + * The pair is the one implied in sbitmap_queue_wake_up() which + * orders clearing sbitmap tag bits and waitqueue_active() in + * __sbitmap_queue_wake_up(), since waitqueue_active() is lockless + * + * Otherwise, re-order of adding wait queue and getting driver tag + * may cause __sbitmap_queue_wake_up() to wake up nothing because + * the waitqueue_active() may not observe us in wait queue. + */ + smp_mb(); + /* * It's possible that a tag was freed in the window between the * allocation failure and adding the hardware queue to the wait