From patchwork Wed Nov 25 06:41:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jingbo Xu X-Patchwork-Id: 11930431 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 745BBC5519F for ; Wed, 25 Nov 2020 06:41:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 372B92075A for ; Wed, 25 Nov 2020 06:41:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725562AbgKYGlx (ORCPT ); Wed, 25 Nov 2020 01:41:53 -0500 Received: from out30-43.freemail.mail.aliyun.com ([115.124.30.43]:39210 "EHLO out30-43.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726034AbgKYGlx (ORCPT ); Wed, 25 Nov 2020 01:41:53 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R891e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=alimailimapcm10staff010182156082;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=5;SR=0;TI=SMTPD_---0UGUIWXH_1606286507; Received: from localhost(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0UGUIWXH_1606286507) by smtp.aliyun-inc.com(127.0.0.1); Wed, 25 Nov 2020 14:41:47 +0800 From: Jeffle Xu To: axboe@kernel.dk Cc: linux-block@vger.kernel.org, joseph.qi@linux.alibaba.com, ming.lei@redhat.com, hch@infradead.org Subject: [PATCH v6] block: disable iopoll for split bio Date: Wed, 25 Nov 2020 14:41:47 +0800 Message-Id: <20201125064147.25389-1-jefflexu@linux.alibaba.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org iopoll is initially for small size, latency sensitive IO. It doesn't work well for big IO, especially when it needs to be split to multiple bios. In this case, the returned cookie of __submit_bio_noacct_mq() is indeed the cookie of the last split bio. The completion of *this* last split bio done by iopoll doesn't mean the whole original bio has completed. Callers of iopoll still need to wait for completion of other split bios. Besides bio splitting may cause more trouble for iopoll which isn't supposed to be used in case of big IO. iopoll for split bio may cause potential race if CPU migration happens during bio submission. Since the returned cookie is that of the last split bio, polling on the corresponding hardware queue doesn't help complete other split bios, if these split bios are enqueued into different hardware queues. Since interrupts are disabled for polling queues, the completion of these other split bios depends on timeout mechanism, thus causing a potential hang. iopoll for split bio may also cause hang for sync polling. Currently both the blkdev and iomap-based fs (ext4/xfs, etc) support sync polling in direct IO routine. These routines will submit bio without REQ_NOWAIT flag set, and then start sync polling in current process context. The process may hang in blk_mq_get_tag() if the submitted bio has to be split into multiple bios and can rapidly exhaust the queue depth. The process are waiting for the completion of the previously allocated requests, which should be reaped by the following polling, and thus causing a deadlock. To avoid these subtle trouble described above, just disable iopoll for split bio. Suggested-by: Ming Lei Signed-off-by: Jeffle Xu Reviewed-by: Christoph Hellwig --- block/bio.c | 2 ++ block/blk-merge.c | 12 ++++++++++++ block/blk-mq.c | 3 +++ include/linux/blk_types.h | 1 + 4 files changed, 18 insertions(+) diff --git a/block/bio.c b/block/bio.c index fa01bef35bb1..7f7ddc22a30d 100644 --- a/block/bio.c +++ b/block/bio.c @@ -684,6 +684,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src) bio_set_flag(bio, BIO_CLONED); if (bio_flagged(bio_src, BIO_THROTTLED)) bio_set_flag(bio, BIO_THROTTLED); + if (bio_flagged(bio_src, BIO_SPLIT)) + bio_set_flag(bio, BIO_SPLIT); bio->bi_opf = bio_src->bi_opf; bio->bi_ioprio = bio_src->bi_ioprio; bio->bi_write_hint = bio_src->bi_write_hint; diff --git a/block/blk-merge.c b/block/blk-merge.c index bcf5e4580603..a2890cebf99f 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -279,6 +279,18 @@ static struct bio *blk_bio_segment_split(struct request_queue *q, return NULL; split: *segs = nsegs; + + /* + * Bio splitting may cause subtle trouble such as hang when doing sync + * iopoll in direct IO routine. Given performance gain of iopoll for + * big IO can be trival, disable iopoll when split needed. We need + * BIO_SPLIT to identify bios need this workaround. Since currently + * only normal IO under mq routine may suffer this issue, BIO_SPLIT is + * only marked here. + */ + bio->bi_opf &= ~REQ_HIPRI; + bio_set_flag(bio, BIO_SPLIT); + return bio_split(bio, sectors, GFP_NOIO, bs); } diff --git a/block/blk-mq.c b/block/blk-mq.c index 55bcee5dc032..ce1f3628e4c2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2265,6 +2265,9 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio) blk_mq_sched_insert_request(rq, false, true, true); } + if (bio_flagged(bio, BIO_SPLIT)) + return BLK_QC_T_NONE; + return cookie; queue_exit: blk_queue_exit(q); diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h index d9b69bbde5cc..528054c5e0bd 100644 --- a/include/linux/blk_types.h +++ b/include/linux/blk_types.h @@ -284,6 +284,7 @@ enum { * of this bio. */ BIO_CGROUP_ACCT, /* has been accounted to a cgroup */ BIO_TRACKED, /* set if bio goes through the rq_qos path */ + BIO_SPLIT, /* bio got split because of queue limits*/ BIO_FLAG_LAST };