From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751773AbZDVEtg (ORCPT ); Wed, 22 Apr 2009 00:49:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750890AbZDVEt0 (ORCPT ); Wed, 22 Apr 2009 00:49:26 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:34396 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750821AbZDVEtZ (ORCPT ); Wed, 22 Apr 2009 00:49:25 -0400 From: KOSAKI Motohiro To: Eric Sandeen Subject: Re: [PATCH, RFC] check for frozen filesystems in the mmap path Cc: kosaki.motohiro@jp.fujitsu.com, linux-fsdevel , Linux Kernel Mailing List , Rik van Riel In-Reply-To: <49EDE319.10701@redhat.com> References: <20090421140045.F125.A69D9226@jp.fujitsu.com> <49EDE319.10701@redhat.com> Message-Id: <20090422132451.62A4.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50 [ja] Date: Wed, 22 Apr 2009 13:49:21 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > 2. this logic kill multi thread application. > > > > this logic mean mmap_sem grabbing until unfreeze. > > it mean othrer thread in the same process can't page-fault although > > it don't touch frozen-sb. > > it seems strange. > > Hm, I hadn't thought about this ... On the one hand, ->page_mkwrite can > already sleep, though a userspace freeze/unfreeze could potentially take > much much longer. freeze/unfreeze *should* happen very quickly, but > nothing enforces that. > > Do you have any suggestions? One more comment. I read ioctl_fsfreeze() and freeze_bdev(), it call __fsync_super(). Oh, I don't think __fsync_suepr is very quick. So, page-fault have one unique characteristics. if page-fault return 0 without pte change, page-fault is occur again soon. then, if you need long time waiting, I think you can use following technique. unlock mmap_sem wait long-time lock mmap_sem goto out; it cause page-fault counter increment twice unintesionally. but no problem. fs-freeze is not freqently event. Am I missing anything?