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Violators will be prosecuted; Tue, 15 May 2018 09:03:43 -0400 Received: from b01ledav004.gho.pok.ibm.com (b01ledav004.gho.pok.ibm.com [9.57.199.109]) by b01cxnp22035.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w4FD3gYl56623168; Tue, 15 May 2018 13:03:42 GMT Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6AA37112034; Tue, 15 May 2018 09:03:45 -0400 (EDT) Received: from pacoca.br.ibm.com (unknown [9.7.47.248]) by b01ledav004.gho.pok.ibm.com (Postfix) with ESMTP id 07FB0112057; Tue, 15 May 2018 09:03:44 -0400 (EDT) From: Jose Ricardo Ziviani To: kernel-team@lists.ubuntu.com Subject: [Bionic][PATCH v3 08/21] blk-mq: make sure hctx->next_cpu is set correctly Date: Tue, 15 May 2018 10:03:11 -0300 X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180515130324.23815-1-joserz@linux.vnet.ibm.com> References: <20180515130324.23815-1-joserz@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 18051513-0044-0000-0000-000004149EB4 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009029; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000260; SDB=6.01032654; UDB=6.00527946; IPR=6.00811785; MB=3.00021126; MTD=3.00000008; XFM=3.00000015; UTC=2018-05-15 13:03:44 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18051513-0045-0000-0000-00000846B2F7 Message-Id: <20180515130324.23815-9-joserz@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2018-05-15_03:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805150132 X-Mailman-Approved-At: Wed, 16 May 2018 17:01:18 +0000 X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.20 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: "kernel-team" From: Ming Lei BugLink: http://bugs.launchpad.net/bugs/1759723 When hctx->next_cpu is set from possible online CPUs, there is one race in which hctx->next_cpu may be set as >= nr_cpu_ids, and finally break workqueue. The race can be triggered in the following two sitations: 1) when one CPU is becoming DEAD, blk_mq_hctx_notify_dead() is called to dispatch requests from the DEAD cpu context, but at that time, this DEAD CPU has been cleared from 'cpu_online_mask', so all CPUs in hctx->cpumask may become offline, and cause hctx->next_cpu set a bad value. 2) blk_mq_delay_run_hw_queue() is called from CPU B, and found the queue should be run on the other CPU A, then CPU A may become offline at the same time and all CPUs in hctx->cpumask become offline. This patch deals with this issue by re-selecting next CPU, and making sure it is set correctly. Cc: Christian Borntraeger Cc: Stefan Haberland Cc: Christoph Hellwig Cc: Thomas Gleixner Reported-by: "jianchao.wang" Tested-by: "jianchao.wang" Fixes: 20e4d81393 ("blk-mq: simplify queue mapping & schedule with each possisble CPU") Signed-off-by: Ming Lei Signed-off-by: Jens Axboe (cherry picked from commit 7bed45954b95601230ebf387d3e4e20e4a3cc025) Signed-off-by: Jose Ricardo Ziviani --- block/blk-mq.c | 30 ++++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/block/blk-mq.c b/block/blk-mq.c index 50ef7dc4c41e..59f4127bdaed 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1257,21 +1257,47 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx) */ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx) { + bool tried = false; + if (hctx->queue->nr_hw_queues == 1) return WORK_CPU_UNBOUND; if (--hctx->next_cpu_batch <= 0) { int next_cpu; - +select_cpu: next_cpu = cpumask_next_and(hctx->next_cpu, hctx->cpumask, cpu_online_mask); if (next_cpu >= nr_cpu_ids) next_cpu = cpumask_first_and(hctx->cpumask,cpu_online_mask); - hctx->next_cpu = next_cpu; + /* + * No online CPU is found, so have to make sure hctx->next_cpu + * is set correctly for not breaking workqueue. + */ + if (next_cpu >= nr_cpu_ids) + hctx->next_cpu = cpumask_first(hctx->cpumask); + else + hctx->next_cpu = next_cpu; hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH; } + /* + * Do unbound schedule if we can't find a online CPU for this hctx, + * and it should only happen in the path of handling CPU DEAD. + */ + if (!cpu_online(hctx->next_cpu)) { + if (!tried) { + tried = true; + goto select_cpu; + } + + /* + * Make sure to re-select CPU next time once after CPUs + * in hctx->cpumask become online again. + */ + hctx->next_cpu_batch = 1; + return WORK_CPU_UNBOUND; + } return hctx->next_cpu; }