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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 B87D9C48BD7 for ; Thu, 27 Jun 2019 19:59:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8FCFC2075E for ; Thu, 27 Jun 2019 19:59:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Opin+Qyd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726505AbfF0T7v (ORCPT ); Thu, 27 Jun 2019 15:59:51 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:41422 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726384AbfF0T7v (ORCPT ); Thu, 27 Jun 2019 15:59:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=1zaJPISJ/EM3luyF1vz7G/5Xji346kDTt6heztPdAbM=; b=Opin+Qydyf8b8u+uTC3Ub0SNO bNiTRXwZJKK3vmcNgV3Q+9ZsiLEpy0Z/TptTzlqTB/at+xjh5msPBhEbfBZw2ume9YxOvHLAyj+mR vneJqGV8dfXGHd2fo6u2nzXrMquEyTDAhcs/rjOCT1tNz10efzK73Zc+asQMhIG2/TKghMpiHcCEt jQMbY9H3RIcg2UIxJBohct5anRwA9gw7fz+Rq2giBj3pqDhWPfqxDk3f6ts7XQjV6A5U21Aq3bcfP eqUCt08yZKTPer3mQ6Bg+Sly5ULCt7EJx5YiuALhtj6Cg2It6s4hByBpQujCnvyeNIeuWALavj14k pspOiFNAg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92 #3 (Red Hat Linux)) id 1hgaYe-0007ij-P9; Thu, 27 Jun 2019 19:59:48 +0000 Date: Thu, 27 Jun 2019 12:59:48 -0700 From: Matthew Wilcox To: Dan Williams Cc: linux-nvdimm , Jan Kara , stable , Robert Barror , Seema Pandit , linux-fsdevel , Linux Kernel Mailing List Subject: Re: [PATCH] filesystem-dax: Disable PMD support Message-ID: <20190627195948.GB4286@bombadil.infradead.org> References: <156159454541.2964018.7466991316059381921.stgit@dwillia2-desk3.amr.corp.intel.com> <20190627123415.GA4286@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Jun 27, 2019 at 12:09:29PM -0700, Dan Williams wrote: > > This bug feels like we failed to unlock, or unlocked the wrong entry > > and this hunk in the bisected commit looks suspect to me. Why do we > > still need to drop the lock now that the radix_tree_preload() calls > > are gone? > > Nevermind, unmapp_mapping_pages() takes a sleeping lock, but then I > wonder why we don't restart the lookup like the old implementation. We have the entry locked: /* * Make sure 'entry' remains valid while we drop * the i_pages lock. */ dax_lock_entry(xas, entry); /* * Besides huge zero pages the only other thing that gets * downgraded are empty entries which don't need to be * unmapped. */ if (dax_is_zero_entry(entry)) { xas_unlock_irq(xas); unmap_mapping_pages(mapping, xas->xa_index & ~PG_PMD_COLOUR, PG_PMD_NR, false); xas_reset(xas); xas_lock_irq(xas); } If something can remove a locked entry, then that would seem like the real bug. Might be worth inserting a lookup there to make sure that it hasn't happened, I suppose?