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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1C530C43334 for ; Wed, 8 Jun 2022 18:22:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234259AbiFHSV5 (ORCPT ); Wed, 8 Jun 2022 14:21:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234109AbiFHSVy (ORCPT ); Wed, 8 Jun 2022 14:21:54 -0400 Received: from ale.deltatee.com (ale.deltatee.com [204.191.154.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9D2EF1C116; Wed, 8 Jun 2022 11:21:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=deltatee.com; s=20200525; h=Subject:In-Reply-To:From:References:Cc:To: MIME-Version:Date:Message-ID:content-disposition; bh=XkHYb+oSLXpBEo6cMCxhRVOvyJgyvCtSljAnI7lNXXs=; b=dMHipBDXa0Xk7SK9ngGdmavKtu 1iGj6Wpj4Oup+A1YqQ38iNCwOd6Z0Dp9AYpaGR6Wodq86/c2sw2fPweXbUW8qf8WUF0p/OjEJpVI0 DmYiI7SVKaCkBEebjgJ4fsaBCakf+w/0HzcENdOY6m5WXlRn5IsJYdsFag/mhpg9AJJTUwSoBEDkZ GNP8av8fYRVGWzCXSeldXEmIW9QkY1BKk5SPjgcR2mHVggTjPLK+D67BEhPT9eVpf4doOsGSSsNec ogK9HDp1Atv+v2LQpzqUGm8EHynoNyyzqyqSTNAHHYiOTgA8dXxqsIAejkeK7DgHIQ6031aM5/tOd u1Y7TwGg==; Received: from s0106ac1f6bb1ecac.cg.shawcable.net ([70.73.163.230] helo=[192.168.11.155]) by ale.deltatee.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94.2) (envelope-from ) id 1nz0JP-0028yT-Ow; Wed, 08 Jun 2022 12:21:48 -0600 Message-ID: <08b80caa-d726-b9f3-7ce0-f486b8080ec5@deltatee.com> Date: Wed, 8 Jun 2022 12:21:46 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Content-Language: en-US To: Song Liu Cc: open list , linux-raid , Christoph Hellwig , Donald Buczek , Guoqing Jiang , Xiao Ni , Stephen Bates , Martin Oliveira , David Sloan , Christoph Hellwig References: <20220608162756.144600-1-logang@deltatee.com> <20220608162756.144600-5-logang@deltatee.com> From: Logan Gunthorpe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 70.73.163.230 X-SA-Exim-Rcpt-To: song@kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, hch@infradead.org, buczek@molgen.mpg.de, guoqing.jiang@linux.dev, xni@redhat.com, sbates@raithlin.com, Martin.Oliveira@eideticom.com, David.Sloan@eideticom.com, hch@lst.de X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v4 04/11] md/raid5: Ensure array is suspended for calls to log_exit() X-SA-Exim-Version: 4.2.1 (built Sat, 13 Feb 2021 17:57:42 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-06-08 11:59, Song Liu wrote: > On Wed, Jun 8, 2022 at 9:28 AM Logan Gunthorpe wrote: >> >> The raid5-cache code relies on there being no IO in flight when >> log_exit() is called. There are two places where this is not >> guaranteed so add mddev_suspend() and mddev_resume() calls to these >> sites. >> >> The site in raid5_remove_disk() has a comment saying that it is >> called in raid5d and thus cannot wait for pending writes; however that >> does not appear to be correct anymore (if it ever was) as >> raid5_remove_disk() is called from hot_remove_disk() which only >> appears to be called in the md_ioctl(). Thus, the comment is removed, >> as well as the racy check and replaced with calls to suspend/resume. >> >> The site in raid5_change_consistency_policy() is in the error path, >> and another similar call site already has suspend/resume calls just >> below it; so it should be equally safe to make that change here. >> >> Signed-off-by: Logan Gunthorpe >> Reviewed-by: Christoph Hellwig >> --- >> drivers/md/raid5.c | 18 ++++++------------ >> 1 file changed, 6 insertions(+), 12 deletions(-) >> >> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c >> index 5d09256d7f81..3ad37dd4c5cd 100644 >> --- a/drivers/md/raid5.c >> +++ b/drivers/md/raid5.c >> @@ -7938,18 +7938,9 @@ static int raid5_remove_disk(struct mddev *mddev, struct md_rdev *rdev) >> >> print_raid5_conf(conf); >> if (test_bit(Journal, &rdev->flags) && conf->log) { >> - /* >> - * we can't wait pending write here, as this is called in >> - * raid5d, wait will deadlock. >> - * neilb: there is no locking about new writes here, >> - * so this cannot be safe. >> - */ >> - if (atomic_read(&conf->active_stripes) || >> - atomic_read(&conf->r5c_cached_full_stripes) || >> - atomic_read(&conf->r5c_cached_partial_stripes)) { >> - return -EBUSY; >> - } >> + mddev_suspend(mddev); > > Unfortunately, the comment about deadlock is still true, and we cannot call > mddev_suspend here. To trigger it: Ah, yes. What a tangle. I think we can just drop this patch. Now that we are removing RCU it isn't actually necessary to fix the bug I was seeing. It's still probably broken as the comment notes though. Thanks, Logan