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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 E73DCC07E96 for ; Thu, 8 Jul 2021 06:58:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C3AF861CD5 for ; Thu, 8 Jul 2021 06:58:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229806AbhGHHBe (ORCPT ); Thu, 8 Jul 2021 03:01:34 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42346 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229735AbhGHHBe (ORCPT ); Thu, 8 Jul 2021 03:01:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1625727531; 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=cDDCLPX/KTvwNQIXz/L6F+rbQsJYne8csUg0Oc3cY28=; b=CRmfcBzUxllzWf6XiVjkqRpFE2ccuvCxc559BKI1qgXf6d+4CMsWFYfA6zRsDlC4Tez7Zs HuYqAZPurF8Nz7+h+w63y2KtN+q2oJdFRvMCRuqwErUieAf6eN6EocQYFFQHfVY04tE+y7 bAWq8K0NNdYUxDm/n6vy4djDQJQb4p0= 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-585-5Y7FuXboMumK-ya2pbOjEw-1; Thu, 08 Jul 2021 02:58:50 -0400 X-MC-Unique: 5Y7FuXboMumK-ya2pbOjEw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 735D4107B47E; Thu, 8 Jul 2021 06:58:49 +0000 (UTC) Received: from T590 (ovpn-12-112.pek2.redhat.com [10.72.12.112]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CE1D310016F7; Thu, 8 Jul 2021 06:58:41 +0000 (UTC) Date: Thu, 8 Jul 2021 14:58:36 +0800 From: Ming Lei To: Dan Schatzberg Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Michal =?iso-8859-1?Q?Koutn=FD?= Subject: Re: [PATCH 6/6] loop: don't add worker into idle list Message-ID: References: <20210705102607.127810-1-ming.lei@redhat.com> <20210705102607.127810-7-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 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Jul 07, 2021 at 09:55:34AM -0400, Dan Schatzberg wrote: > On Wed, Jul 07, 2021 at 11:19:14AM +0800, Ming Lei wrote: > > On Tue, Jul 06, 2021 at 09:55:36AM -0400, Dan Schatzberg wrote: > > > On Mon, Jul 05, 2021 at 06:26:07PM +0800, Ming Lei wrote: > > > > } > > > > + > > > > + spin_lock(lock); > > > > list_add_tail(&cmd->list_entry, cmd_list); > > > > + spin_unlock(lock); > > > > queue_work(lo->workqueue, work); > > > > - spin_unlock(&lo->lo_work_lock); > > > > } > > > > > > > > static void loop_update_rotational(struct loop_device *lo) > > > > @@ -1131,20 +1159,18 @@ static void loop_set_timer(struct loop_device *lo) > > > > > > > > static void __loop_free_idle_workers(struct loop_device *lo, bool force) > > > > { > > > > - struct loop_worker *pos, *worker; > > > > + struct loop_worker *worker; > > > > + unsigned long id; > > > > > > > > spin_lock(&lo->lo_work_lock); > > > > - list_for_each_entry_safe(worker, pos, &lo->idle_worker_list, > > > > - idle_list) { > > > > + xa_for_each(&lo->workers, id, worker) { > > > > if (!force && time_is_after_jiffies(worker->last_ran_at + > > > > LOOP_IDLE_WORKER_TIMEOUT)) > > > > break; > > > > - list_del(&worker->idle_list); > > > > - xa_erase(&lo->workers, worker->blkcg_css->id); > > > > - css_put(worker->blkcg_css); > > > > - kfree(worker); > > > > + if (refcount_dec_and_test(&worker->refcnt)) > > > > + loop_release_worker(worker); > > > > > > This one is puzzling to me. Can't you hit this refcount decrement > > > superfluously each time the loop timer fires? > > > > Not sure I get your point. > > > > As I mentioned above, this one is the counter pair of INIT reference, > > but one new lo_cmd may just grab it when queueing rq before erasing the > > worker from xarray, so we can't release worker here until the command is > > completed. > > Suppose at this point there's still an outstanding loop_cmd to be > serviced for this worker. The refcount_dec_and_test should decrement > the refcount and then fail the conditional, not calling > loop_release_worker. What happens if __loop_free_idle_workers fires > again before the loop_cmd is processed? Won't you decrement the > refcount again, and then end up calling loop_release_worker before the > loop_cmd is processed? Good catch! The following one line change should avoid the issue: diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 146eaa03629b..3cd51bddfec9 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -980,7 +980,6 @@ static struct loop_worker *loop_alloc_or_get_worker(struct loop_device *lo, static void loop_release_worker(struct loop_worker *worker) { - xa_erase(&worker->lo->workers, worker->blkcg_css->id); css_put(worker->blkcg_css); kfree(worker); } @@ -1167,6 +1166,7 @@ static void __loop_free_idle_workers(struct loop_device *lo, bool force) if (!force && time_is_after_jiffies(worker->last_ran_at + LOOP_IDLE_WORKER_TIMEOUT)) break; + xa_erase(&worker->lo->workers, worker->blkcg_css->id); if (refcount_dec_and_test(&worker->refcnt)) loop_release_worker(worker); } Thanks, Ming