From patchwork Thu May 20 22:33:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 12271449 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 7A16EC433ED for ; Thu, 20 May 2021 22:34:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E7AF613AC for ; Thu, 20 May 2021 22:34:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231565AbhETWfZ (ORCPT ); Thu, 20 May 2021 18:35:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:39202 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231533AbhETWfY (ORCPT ); Thu, 20 May 2021 18:35:24 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 90103ABF6; Thu, 20 May 2021 22:34:01 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 365C51F2C5D; Fri, 21 May 2021 00:34:01 +0200 (CEST) From: Jan Kara To: Jens Axboe Cc: , Khazhy Kumykov , Paolo Valente , Jan Kara Subject: [PATCH 1/2] block: Do not merge recursively in elv_attempt_insert_merge() Date: Fri, 21 May 2021 00:33:52 +0200 Message-Id: <20210520223353.11561-2-jack@suse.cz> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210520223353.11561-1-jack@suse.cz> References: <20210520223353.11561-1-jack@suse.cz> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Most of the merging happens at bio level. There should not be much merging happening at request level anymore. Furthermore if we backmerged a request to the previous one, the chances to be able to merge the result to even previous request are slim - that could succeed only if requests were inserted in 2 1 3 order. Merging more requests in elv_attempt_insert_merge() will be difficult to handle when we want to pass requests to free back to the caller of blk_mq_sched_try_insert_merge(). So just remove the possibility of merging multiple requests in elv_attempt_insert_merge(). Signed-off-by: Jan Kara --- block/elevator.c | 19 +++++-------------- 1 file changed, 5 insertions(+), 14 deletions(-) diff --git a/block/elevator.c b/block/elevator.c index 440699c28119..098f4bd226f5 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -350,12 +350,11 @@ enum elv_merge elv_merge(struct request_queue *q, struct request **req, * we can append 'rq' to an existing request, so we can throw 'rq' away * afterwards. * - * Returns true if we merged, false otherwise + * Returns true if we merged, false otherwise. */ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq) { struct request *__rq; - bool ret; if (blk_queue_nomerges(q)) return false; @@ -369,21 +368,13 @@ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq) if (blk_queue_noxmerges(q)) return false; - ret = false; /* * See if our hash lookup can find a potential backmerge. */ - while (1) { - __rq = elv_rqhash_find(q, blk_rq_pos(rq)); - if (!__rq || !blk_attempt_req_merge(q, __rq, rq)) - break; - - /* The merged request could be merged with others, try again */ - ret = true; - rq = __rq; - } - - return ret; + __rq = elv_rqhash_find(q, blk_rq_pos(rq)); + if (!__rq || !blk_attempt_req_merge(q, __rq, rq)) + return false; + return true; } void elv_merged_request(struct request_queue *q, struct request *rq, From patchwork Thu May 20 22:33:53 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 12271453 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 27DACC43461 for ; Thu, 20 May 2021 22:34:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0A260613B6 for ; Thu, 20 May 2021 22:34:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231466AbhETWfZ (ORCPT ); Thu, 20 May 2021 18:35:25 -0400 Received: from mx2.suse.de ([195.135.220.15]:39200 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231524AbhETWfY (ORCPT ); Thu, 20 May 2021 18:35:24 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 90926AF0C; Thu, 20 May 2021 22:34:01 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 384521F2C9E; Fri, 21 May 2021 00:34:01 +0200 (CEST) From: Jan Kara To: Jens Axboe Cc: , Khazhy Kumykov , Paolo Valente , Jan Kara Subject: [PATCH 2/2] blk: Fix lock inversion between ioc lock and bfqd lock Date: Fri, 21 May 2021 00:33:53 +0200 Message-Id: <20210520223353.11561-3-jack@suse.cz> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20210520223353.11561-1-jack@suse.cz> References: <20210520223353.11561-1-jack@suse.cz> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Lockdep complains about lock inversion between ioc->lock and bfqd->lock: bfqd -> ioc: put_io_context+0x33/0x90 -> ioc->lock grabbed blk_mq_free_request+0x51/0x140 blk_put_request+0xe/0x10 blk_attempt_req_merge+0x1d/0x30 elv_attempt_insert_merge+0x56/0xa0 blk_mq_sched_try_insert_merge+0x4b/0x60 bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed blk_mq_sched_insert_requests+0xd6/0x2b0 blk_mq_flush_plug_list+0x154/0x280 blk_finish_plug+0x40/0x60 ext4_writepages+0x696/0x1320 do_writepages+0x1c/0x80 __filemap_fdatawrite_range+0xd7/0x120 sync_file_range+0xac/0xf0 ioc->bfqd: bfq_exit_icq+0xa3/0xe0 -> bfqd->lock grabbed put_io_context_active+0x78/0xb0 -> ioc->lock grabbed exit_io_context+0x48/0x50 do_exit+0x7e9/0xdd0 do_group_exit+0x54/0xc0 To avoid this inversion we change blk_mq_sched_try_insert_merge() to not free the merged request but rather leave that upto the caller similarly to blk_mq_sched_try_merge(). And in bfq_insert_requests() we make sure to free the request after dropping bfqd->lock. As a nice consequence, this also makes locking rules in bfq_finish_requeue_request() more consistent. Fixes: aee69d78dec0 ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler") Signed-off-by: Jan Kara --- block/bfq-iosched.c | 20 +++++++------------- block/blk-merge.c | 19 ++++++++----------- block/blk.h | 2 +- block/mq-deadline.c | 4 +++- 4 files changed, 19 insertions(+), 26 deletions(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index acd1f881273e..4afdf0b93124 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2317,9 +2317,9 @@ static bool bfq_bio_merge(struct request_queue *q, struct bio *bio, ret = blk_mq_sched_try_merge(q, bio, nr_segs, &free); + spin_unlock_irq(&bfqd->lock); if (free) blk_mq_free_request(free); - spin_unlock_irq(&bfqd->lock); return ret; } @@ -5933,6 +5933,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, spin_lock_irq(&bfqd->lock); if (blk_mq_sched_try_insert_merge(q, rq)) { spin_unlock_irq(&bfqd->lock); + blk_put_request(rq); return; } @@ -6376,6 +6377,7 @@ static void bfq_finish_requeue_request(struct request *rq) { struct bfq_queue *bfqq = RQ_BFQQ(rq); struct bfq_data *bfqd; + unsigned long flags; /* * rq either is not associated with any icq, or is an already @@ -6393,18 +6395,12 @@ static void bfq_finish_requeue_request(struct request *rq) rq->io_start_time_ns, rq->cmd_flags); + spin_lock_irqsave(&bfqd->lock, flags); if (likely(rq->rq_flags & RQF_STARTED)) { - unsigned long flags; - - spin_lock_irqsave(&bfqd->lock, flags); - if (rq == bfqd->waited_rq) bfq_update_inject_limit(bfqd, bfqq); bfq_completed_request(bfqq, bfqd); - bfq_finish_requeue_request_body(bfqq); - - spin_unlock_irqrestore(&bfqd->lock, flags); } else { /* * Request rq may be still/already in the scheduler, @@ -6414,18 +6410,16 @@ static void bfq_finish_requeue_request(struct request *rq) * inconsistencies in the time interval from the end * of this function to the start of the deferred work. * This situation seems to occur only in process - * context, as a consequence of a merge. In the - * current version of the code, this implies that the - * lock is held. + * context, as a consequence of a merge. */ - if (!RB_EMPTY_NODE(&rq->rb_node)) { bfq_remove_request(rq->q, rq); bfqg_stats_update_io_remove(bfqq_group(bfqq), rq->cmd_flags); } - bfq_finish_requeue_request_body(bfqq); } + bfq_finish_requeue_request_body(bfqq); + spin_unlock_irqrestore(&bfqd->lock, flags); /* * Reset private fields. In case of a requeue, this allows diff --git a/block/blk-merge.c b/block/blk-merge.c index 4d97fb6dd226..1398b52a24b4 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -846,18 +846,15 @@ static struct request *attempt_front_merge(struct request_queue *q, return NULL; } -int blk_attempt_req_merge(struct request_queue *q, struct request *rq, - struct request *next) +/* + * Try to merge 'next' into 'rq'. Return true if the merge happened, false + * otherwise. The caller is responsible for freeing 'next' if the merge + * happened. + */ +bool blk_attempt_req_merge(struct request_queue *q, struct request *rq, + struct request *next) { - struct request *free; - - free = attempt_merge(q, rq, next); - if (free) { - blk_put_request(free); - return 1; - } - - return 0; + return attempt_merge(q, rq, next); } bool blk_rq_merge_ok(struct request *rq, struct bio *bio) diff --git a/block/blk.h b/block/blk.h index 8b3591aee0a5..99ef4f7e7a70 100644 --- a/block/blk.h +++ b/block/blk.h @@ -225,7 +225,7 @@ ssize_t part_timeout_store(struct device *, struct device_attribute *, void __blk_queue_split(struct bio **bio, unsigned int *nr_segs); int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs); -int blk_attempt_req_merge(struct request_queue *q, struct request *rq, +bool blk_attempt_req_merge(struct request_queue *q, struct request *rq, struct request *next); unsigned int blk_recalc_rq_segments(struct request *rq); void blk_rq_set_mixed_merge(struct request *rq); diff --git a/block/mq-deadline.c b/block/mq-deadline.c index 8eea2cbf2bf4..64dd78005ae6 100644 --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -494,8 +494,10 @@ static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, */ blk_req_zone_write_unlock(rq); - if (blk_mq_sched_try_insert_merge(q, rq)) + if (blk_mq_sched_try_insert_merge(q, rq)) { + blk_put_request(rq); return; + } trace_block_rq_insert(rq);