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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 79AADC4338F for ; Wed, 18 Aug 2021 01:55:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 50C5F60F38 for ; Wed, 18 Aug 2021 01:55:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235650AbhHRB4J (ORCPT ); Tue, 17 Aug 2021 21:56:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:58472 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233380AbhHRB4J (ORCPT ); Tue, 17 Aug 2021 21:56:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629251734; 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=EM1nHH5NN+DAtSFriY9sgrrbD3ppU2zu52GsYJO9nIg=; b=AX/EEutxhAEWK+iQ7dqkFQFAt5Gfq7YlWBslzmD8JHTG6zffV6Q3jDVhOLouLnlv+170TG m0xGnPKO0M/rYcp0VMgU2mhVuBUBmENLcg9RgAomm1hvnHxxh47F7rMYemVM+CuZSpGR6y kxBnxdMIIQVIPGx5QmkVpcccnyDqzUg= Received: from mail-ej1-f69.google.com (mail-ej1-f69.google.com [209.85.218.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-337-Z1yfUMHLPByGdIfeHcXfPQ-1; Tue, 17 Aug 2021 21:55:31 -0400 X-MC-Unique: Z1yfUMHLPByGdIfeHcXfPQ-1 Received: by mail-ej1-f69.google.com with SMTP id v19-20020a170906b013b02905b2f1bbf8f3so284822ejy.6 for ; Tue, 17 Aug 2021 18:55:31 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=EM1nHH5NN+DAtSFriY9sgrrbD3ppU2zu52GsYJO9nIg=; b=P1ueZHiqsA65MmkzW/rQJAhF4VygqjXSElY3/9LMl7eCOL7WJq+9dJQb3ww+rZzziU qElnB3pZdc83MNPswczq3ANLtv6AJJ0rsjOvgEz3qLMB8ItUi+R9bjasl4ulH7uxMb0/ sIQLmshKeqLXl3yJFoP6O9GIGrF3zFGzfvyDVAn1qqeikBNIm9h77YYZc7QREjTTG4YE n9YemhrRGxJCSkdh1pNpVhRtRgyMT7QUBfeNZl9hUMm1c/gBoZH7QWVK5Ldjy+eOj8mb d3XC+PTfpqDamPB5LoLfL056HhYdSw4tWBTcklWxWLYIXsRC/KzPaPhSwb4H7xNg1GNy XWTQ== X-Gm-Message-State: AOAM5306+j0fjxfllk/YpDdGkmum7430V/6Xjy/dmeo0VLgL11tZtV77 syn5zBnNEl7ov4Qp9lvOCqEhKpoEIRGyzqZP48sbVKwmsadFE+D8Ty+dBlBIZZKdjkN8skqZgwy 5Xb2IeXYt9GORHSaD14aCtXzzErz115hEoYVRFA== X-Received: by 2002:aa7:de05:: with SMTP id h5mr7402045edv.174.1629251730144; Tue, 17 Aug 2021 18:55:30 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw4GTAACmnJe60sd4LFJX1PSl2D6nADyuqTd9hoO4Avc3qTEmM/ZeZtIdG8gkzG9qm2B0oOtj9d9gvU58A5Ge0= X-Received: by 2002:aa7:de05:: with SMTP id h5mr7402037edv.174.1629251730019; Tue, 17 Aug 2021 18:55:30 -0700 (PDT) MIME-Version: 1.0 References: <1629250612-4952-1-git-send-email-xni@redhat.com> In-Reply-To: From: Xiao Ni Date: Wed, 18 Aug 2021 09:55:18 +0800 Message-ID: Subject: Re: [PATCH 1/1] md/raid10: Remove rcu_dereference when it doesn't need rcu lock to protect To: Guoqing Jiang Cc: Song Liu , Nigel Croxon , linux-raid Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-raid@vger.kernel.org On Wed, Aug 18, 2021 at 9:44 AM Guoqing Jiang wrote: > > > > On 8/18/21 9:36 AM, Xiao Ni wrote: > > One warning message is triggered like this: > > [ 695.110751] ============================= > > [ 695.131439] WARNING: suspicious RCU usage > > [ 695.151389] 4.18.0-319.el8.x86_64+debug #1 Not tainted > > [ 695.174413] ----------------------------- > > [ 695.192603] drivers/md/raid10.c:1776 suspicious > > rcu_dereference_check() usage! > > [ 695.225107] other info that might help us debug this: > > [ 695.260940] rcu_scheduler_active = 2, debug_locks = 1 > > [ 695.290157] no locks held by mkfs.xfs/10186. > > > > In the first loop of function raid10_handle_discard. It already > > determines which disk need to handle discard request and add the > > rdev reference count rdev->nr_pending. So the conf->mirrors will > > not change until all bios come back from underlayer disks. It > > doesn't need to use rcu_dereference to get rdev. > > > > Fixes: d30588b2731f ('md/raid10: improve raid10 discard request') > > Signed-off-by: Xiao Ni > > --- > > drivers/md/raid10.c | 13 +++++++++---- > > 1 file changed, 9 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c > > index 16977e8..1d3ac76 100644 > > --- a/drivers/md/raid10.c > > +++ b/drivers/md/raid10.c > > @@ -1712,6 +1712,10 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio) > > } else > > r10_bio->master_bio = (struct bio *)first_r10bio; > > > > + /* first select target devices under rcu_lock and > > + * inc refcount on their rdev. Record them by setting > > + * bios[x] to bio > > + */ > > Nit: the comment style is not correct. Hi Guoqing /* * first select target devices under rcu_lock and * inc refcount on their rdev. Record them by setting * bios[x] to bio */ It should be like this, right? If so, I'll send v2 and add your ack in the patch too.