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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 EE7A6C43387 for ; Wed, 19 Dec 2018 16:12:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC8062084A for ; Wed, 19 Dec 2018 16:12:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727613AbeLSQMC (ORCPT ); Wed, 19 Dec 2018 11:12:02 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727252AbeLSQMC (ORCPT ); Wed, 19 Dec 2018 11:12:02 -0500 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CF05F3DE; Wed, 19 Dec 2018 16:12:01 +0000 (UTC) Received: from localhost (unknown [10.18.25.149]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E57EA6B465; Wed, 19 Dec 2018 16:11:58 +0000 (UTC) Date: Wed, 19 Dec 2018 11:11:58 -0500 From: Mike Snitzer To: Jens Axboe Cc: "linux-block@vger.kernel.org" , Ming Lei , Dennis Zhou Subject: Re: dm: don't reuse bio for flushes Message-ID: <20181219161157.GA29426@redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 19 Dec 2018 16:12:01 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Dec 19 2018 at 10:50am -0500, Jens Axboe wrote: > DM currently has a statically allocated bio that it uses to issue empty > flushes. It doesn't submit this bio, it just uses it for maintaining > state while setting up clones. Multiple users can access this bio at the > same time. This wasn't previously an issue, even if it was a bit iffy, > but with the blkg associations it can become one. > > We setup the blkg association, then clone bio's and submit, then remove > the blkg assocation again. But since we can have multiple tasks doing > this at the same time, against multiple blkg's, then we can either lose > references to a blkg, or put it twice. The latter causes complaints on > the percpu ref being <= 0 when released, and can cause use-after-free as > well. Ming reports that xfstest generic/475 triggers this: > > ------------[ cut here ]------------ > percpu ref (blkg_release) <= 0 (0) after switching to atomic > WARNING: CPU: 13 PID: 0 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x2c9/0x4a0 > > Switch to just using an on-stack bio for this, and get rid of the > embedded bio. > > Fixes: 5cdf2e3fea5e ("blkcg: associate blkg when associating a device") > Reported-by: Ming Lei > Signed-off-by: Jens Axboe Thanks for sorting this one out, definitely wasn't happy with how exposed DM was left with the recent blkg changes. This is clearly better. Acked-by: Mike Snitzer