From mboxrd@z Thu Jan 1 00:00:00 1970 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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 6A6B2C433ED for ; Wed, 28 Apr 2021 00:07:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2E64A61401 for ; Wed, 28 Apr 2021 00:07:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230460AbhD1AIf (ORCPT ); Tue, 27 Apr 2021 20:08:35 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:45317 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237104AbhD1AIe (ORCPT ); Tue, 27 Apr 2021 20:08:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619568470; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=uZsmYhCuHp1hFHjSy9V32ap7TaQ8LBlpLfQl9JtaTMw=; b=e4RQlc4ixF+V9ZFgbuN5BVcedOotHiJ+uhIEy3n0criRQ+WWJc2kkU6gAYZ/RpHHdoLPuk AnGQzHgTmv5OMIM0mv9ouZODOmdnCGoouRMdDeCL1C0jZatF+KWDCRZ95OupLnIBhj7ewj G2cI2KUHh//GbSnoT2F7BTfYKtZVxnY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-154-1joyMRP0PhezsqBCmXEalA-1; Tue, 27 Apr 2021 20:07:49 -0400 X-MC-Unique: 1joyMRP0PhezsqBCmXEalA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E17139126F; Wed, 28 Apr 2021 00:07:47 +0000 (UTC) Received: from T590 (ovpn-12-77.pek2.redhat.com [10.72.12.77]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3E1FA5D6D5; Wed, 28 Apr 2021 00:07:39 +0000 (UTC) Date: Wed, 28 Apr 2021 08:07:47 +0800 From: Ming Lei To: Bart Van Assche Cc: Jens Axboe , linux-block@vger.kernel.org, Khazhy Kumykov , Shin'ichiro Kawasaki , Hannes Reinecke , John Garry , David Jeffery Subject: Re: [PATCH V3 2/3] blk-mq: grab rq->refcount before calling ->fn in blk_mq_tagset_busy_iter Message-ID: References: <20210427151058.2833168-1-ming.lei@redhat.com> <20210427151058.2833168-3-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Apr 27, 2021 at 01:17:06PM -0700, Bart Van Assche wrote: > On 4/27/21 8:10 AM, Ming Lei wrote: > > +void blk_mq_put_rq_ref(struct request *rq) > > +{ > > + if (is_flush_rq(rq, rq->mq_hctx)) > > + rq->end_io(rq, 0); > > + else if (refcount_dec_and_test(&rq->ref)) > > + __blk_mq_free_request(rq); > > +} > > The above function needs more work. blk_mq_put_rq_ref() may be called from > multiple CPUs concurrently and hence must handle concurrent calls safely. > The flush .end_io callbacks have not been designed to handle concurrent > calls. static void flush_end_io(struct request *flush_rq, blk_status_t error) { struct request_queue *q = flush_rq->q; struct list_head *running; struct request *rq, *n; unsigned long flags = 0; struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx); /* release the tag's ownership to the req cloned from */ spin_lock_irqsave(&fq->mq_flush_lock, flags); if (!refcount_dec_and_test(&flush_rq->ref)) { fq->rq_status = error; spin_unlock_irqrestore(&fq->mq_flush_lock, flags); return; } ... spin_unlock_irqrestore(&fq->mq_flush_lock, flags); } Both spin lock and refcount_dec_and_test() are called at the beginning of flush_end_io(), so it is absolutely reliable in case of concurrent calls. Otherwise, it is simply one issue between normal completion and timeout since the pattern in this patch is same with timeout. Or do I miss something? Thanks, Ming