From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 C02E9DF6A for ; Thu, 9 Nov 2023 07:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pC+MYQ0q" Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12B42271F for ; Wed, 8 Nov 2023 23:30:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=3TbkP6dPgG5rg1ywx3LROqX2NH5sWqW+beHjo4sUY+8=; b=pC+MYQ0q8CtnIJnrToXKam9cwQ R9vFpPVWTQQFk9swJiA+B8rzHL+QXMA7JSq1zprZUeSSEg8/CarNDW73Co3Avg8qVI31U3KgBBQSv QvsPCyKqId5woXXyYf57TsTkbhlKk5JNdpI8tWzu7MyS/tI5ZTEhJZcmp01mblizOzB/rJ7zYVG0I SVfslDuV9YPTtOUhQ+S6tXrPDFbaB2K8DZKMXM6Icgdo1kCWIId4QRibmHvmKEEjzeDzj1hgk0P2W AsH7w8qQ7zqC4piEEjJkvOJl0TbCLS077fC7CRwRM0Gfv/Mi5CasmSLquLqQHdRDYLj0kHLiJ3fEG E/rLt6bA==; Received: from hch by bombadil.infradead.org with local (Exim 4.96 #2 (Red Hat Linux)) id 1r0zUQ-005VSI-0I; Thu, 09 Nov 2023 07:30:10 +0000 Date: Wed, 8 Nov 2023 23:30:10 -0800 From: Christoph Hellwig To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Yi Zhang Subject: Re: [PATCH] blk-mq: make sure active queue usage is held for bio_integrity_prep() Message-ID: References: <20231108080504.2144952-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231108080504.2144952-1-ming.lei@redhat.com> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html > +++ b/block/blk-mq.c > @@ -2858,11 +2858,8 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q, > }; > struct request *rq; > > - if (unlikely(bio_queue_enter(bio))) > - return NULL; > - > if (blk_mq_attempt_bio_merge(q, bio, nsegs)) > - goto queue_exit; > + return NULL; > > rq_qos_throttle(q, bio); For clarity splitting this out might be a bit more readable. > +static inline struct request *blk_mq_cached_req(const struct request_queue *q, > + const struct blk_plug *plug) > +{ > + if (plug) { > + struct request *rq = rq_list_peek(&plug->cached_rq); > + > + if (rq && rq->q == q) > + return rq; > + } > + return NULL; > +} Not sure this helper adds much value over just open coding it. > +/* return true if this bio needs to handle by allocating new request */ > +static inline bool blk_mq_try_cached_rq(struct request *rq, > struct blk_plug *plug, struct bio **bio, unsigned int nsegs) The polarity here is a bit weird, I'd expect a true return if the request can be used and a naming implying that. > + rq = blk_mq_cached_req(q, plug); > + if (rq) { > + /* cached request held queue usage counter */ > + if (!bio_integrity_prep(bio)) > + return; > + > + need_alloc = blk_mq_try_cached_rq(rq, plug, &bio, nr_segs); > if (!bio) > return; If you take the blk_mq_attempt_bio_merge merge out of the helper, the calling convention becomes much saner. > + /* cached request held queue usage counter */ > + percpu_ref_get(&q->q_usage_counter); I don't think we can just do the percpu_ref_get here. While getting the counter obviosuly can't fail, we still need to do the queue pm only check. Below is the untested version of how I'd do this that I hacked while reviewing it: --- commit 1134ce39504c30a9804ed8147027e66bf7d3157e Author: Ming Lei Date: Wed Nov 8 16:05:04 2023 +0800 blk-mq: make sure active queue usage is held for bio_integrity_prep() blk_integrity_unregister() can come if queue usage counter isn't held for one bio with integrity prepared, so this request may be completed with calling profile->complete_fn, then kernel panic. Another constraint is that bio_integrity_prep() needs to be called before bio merge. Fix the issue by: - call bio_integrity_prep() with one queue usage counter grabbed reliably - call bio_integrity_prep() before bio merge Fixes: 900e080752025f00 ("block: move queue enter logic into blk_mq_submit_bio()") Reported-by: Yi Zhang Signed-off-by: Ming Lei diff --git a/block/blk-mq.c b/block/blk-mq.c index e2d11183f62e37..b758dc8ed10957 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -2858,11 +2858,8 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q, }; struct request *rq; - if (unlikely(bio_queue_enter(bio))) - return NULL; - if (blk_mq_attempt_bio_merge(q, bio, nsegs)) - goto queue_exit; + return NULL; rq_qos_throttle(q, bio); @@ -2878,35 +2875,24 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q, rq_qos_cleanup(q, bio); if (bio->bi_opf & REQ_NOWAIT) bio_wouldblock_error(bio); -queue_exit: - blk_queue_exit(q); return NULL; } -static inline struct request *blk_mq_get_cached_request(struct request_queue *q, - struct blk_plug *plug, struct bio **bio, unsigned int nsegs) +/* return true if this @rq can be used for @bio */ +static bool blk_mq_can_use_cached_rq(struct request *rq, struct blk_plug *plug, + struct bio *bio) { - struct request *rq; - enum hctx_type type, hctx_type; + struct request_queue *q = rq->q; + enum hctx_type type = blk_mq_get_hctx_type(bio->bi_opf); + enum hctx_type hctx_type = rq->mq_hctx->type; - if (!plug) - return NULL; - rq = rq_list_peek(&plug->cached_rq); - if (!rq || rq->q != q) - return NULL; + WARN_ON_ONCE(rq_list_peek(&plug->cached_rq) != rq); - if (blk_mq_attempt_bio_merge(q, *bio, nsegs)) { - *bio = NULL; - return NULL; - } - - type = blk_mq_get_hctx_type((*bio)->bi_opf); - hctx_type = rq->mq_hctx->type; if (type != hctx_type && !(type == HCTX_TYPE_READ && hctx_type == HCTX_TYPE_DEFAULT)) - return NULL; - if (op_is_flush(rq->cmd_flags) != op_is_flush((*bio)->bi_opf)) - return NULL; + return false; + if (op_is_flush(rq->cmd_flags) != op_is_flush(bio->bi_opf)) + return false; /* * If any qos ->throttle() end up blocking, we will have flushed the @@ -2914,12 +2900,12 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q, * before we throttle. */ plug->cached_rq = rq_list_next(rq); - rq_qos_throttle(q, *bio); + rq_qos_throttle(q, bio); blk_mq_rq_time_init(rq, 0); - rq->cmd_flags = (*bio)->bi_opf; + rq->cmd_flags = bio->bi_opf; INIT_LIST_HEAD(&rq->queuelist); - return rq; + return true; } static void bio_set_ioprio(struct bio *bio) @@ -2949,7 +2935,7 @@ void blk_mq_submit_bio(struct bio *bio) struct blk_plug *plug = blk_mq_plug(bio); const int is_sync = op_is_sync(bio->bi_opf); struct blk_mq_hw_ctx *hctx; - struct request *rq; + struct request *rq = NULL; unsigned int nr_segs = 1; blk_status_t ret; @@ -2960,20 +2946,39 @@ void blk_mq_submit_bio(struct bio *bio) return; } - if (!bio_integrity_prep(bio)) - return; - bio_set_ioprio(bio); - rq = blk_mq_get_cached_request(q, plug, &bio, nr_segs); - if (!rq) { - if (!bio) + if (plug) { + rq = rq_list_peek(&plug->cached_rq); + if (rq && rq->q != q) + rq = NULL; + } + if (rq) { + /* rq already holds a q_usage_counter reference */ + if (!bio_integrity_prep(bio)) return; - rq = blk_mq_get_new_requests(q, plug, bio, nr_segs); - if (unlikely(!rq)) + if (blk_mq_attempt_bio_merge(q, bio, nr_segs)) + return; + + if (blk_mq_can_use_cached_rq(rq, plug, bio)) + goto done; + + percpu_ref_get(&q->q_usage_counter); + } else { + if (unlikely(bio_queue_enter(bio))) + return; + + if (!bio_integrity_prep(bio)) return; } + rq = blk_mq_get_new_requests(q, plug, bio, nr_segs); + if (unlikely(!rq)) { + blk_queue_exit(q); + return; + } + +done: trace_block_getrq(bio); rq_qos_track(q, rq, bio);