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=-2.4 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 89AE3C65BAE for ; Thu, 13 Dec 2018 16:01:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 589FF20851 for ; Thu, 13 Dec 2018 16:01:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 589FF20851 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729201AbeLMQBX (ORCPT ); Thu, 13 Dec 2018 11:01:23 -0500 Received: from mx2.suse.de ([195.135.220.15]:33674 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727942AbeLMQBW (ORCPT ); Thu, 13 Dec 2018 11:01:22 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id A7132AED2; Thu, 13 Dec 2018 16:01:20 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 518BF1E13E6; Thu, 13 Dec 2018 17:01:18 +0100 (CET) Date: Thu, 13 Dec 2018 17:01:18 +0100 From: Jan Kara To: Andrew Morton Cc: Josef Bacik , kernel-team@fb.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, tj@kernel.org, david@fromorbit.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, riel@redhat.com, jack@suse.cz Subject: Re: [PATCH][v6] filemap: drop the mmap_sem for all blocking operations Message-ID: <20181213160118.GA27517@quack2.suse.cz> References: <20181211173801.29535-4-josef@toxicpanda.com> <20181212152757.10017-1-josef@toxicpanda.com> <20181212155536.5fb770a0c9b4f2399d4794e4@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181212155536.5fb770a0c9b4f2399d4794e4@linux-foundation.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 12-12-18 15:55:36, Andrew Morton wrote: > On Wed, 12 Dec 2018 10:27:57 -0500 Josef Bacik wrote: > > > v5->v6: > > - added more comments as per Andrew's suggestion. > > - fixed the fpin leaks in the two error paths that were pointed out. > > > > hm, > > > --- a/mm/filemap.c~filemap-drop-the-mmap_sem-for-all-blocking-operations-v6 > > +++ a/mm/filemap.c > > @@ -2461,7 +2476,8 @@ static struct file *do_sync_mmap_readahe > > > > /* > > * Asynchronous readahead happens when we find the page and PG_readahead, > > - * so we want to possibly extend the readahead further.. > > + * so we want to possibly extend the readahead further. We return the file that > > + * was pinned if we have to drop the mmap_sem in order to do IO. > > */ > > static struct file *do_async_mmap_readahead(struct vm_fault *vmf, > > struct page *page) > > @@ -2545,14 +2561,15 @@ retry_find: > > page = pagecache_get_page(mapping, offset, > > FGP_CREAT|FGP_FOR_MMAP, > > vmf->gfp_mask); > > - if (!page) > > + if (!page) { > > + if (fpin) > > + goto out_retry; > > Is this right? If pagecache_get_page() returns NULL we can now return > VM_FAULT_MAJOR|VM_FAULT_RETRY whereas we used to return ENOMEM. Yes, but once we've dropped mmap_sem, there's no way safely return -ENOMEM. So VM_FAULT_RETRY is really the only option to tell the caller that mmap_sem is not held anymore... So the patch looks good to me now. You can add: Reviewed-by: Jan Kara Honza -- Jan Kara SUSE Labs, CR