From: Arnd Bergmann Subject: Re: Y2038 bug in ext4 recently_deleted() function Date: Tue, 22 Aug 2017 17:18:14 +0200 Message-ID: References: <20170808050517.7160-1-wshilong@ddn.com> <20170816164211.GA31117@quack2.suse.cz> <3ED34739A4E85E4F894367D57617CDEFEDA401CE@LAX-EX-MB2.datadirect.datadirectnet.com> <20170817091959.GB7644@quack2.suse.cz> <20170817092153.GA14074@quack2.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Deepa Dinamani , "Theodore Ts'o" , Wang Shilong , Wang Shilong , "linux-ext4@vger.kernel.org" , Shuichi Ihara , Li Xi , Jan Kara To: Andreas Dilger Return-path: Received: from mail-oi0-f51.google.com ([209.85.218.51]:34774 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932815AbdHVPSP (ORCPT ); Tue, 22 Aug 2017 11:18:15 -0400 Received: by mail-oi0-f51.google.com with SMTP id j144so61048297oib.1 for ; Tue, 22 Aug 2017 08:18:14 -0700 (PDT) In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, Aug 18, 2017 at 6:09 PM, Andreas Dilger wrote: > >>>> So moving to the case of a 32 bit machine: >>>> >>>> get_seconds() can return values until year 2106. And, recentcy at max >>>> can only be 35. Analyzing the current line: >>>> >>>> if (dtime && (dtime < now) && (now < dtime + recentcy)) >>>> >>>> The above equation should work fine at least until 35 seconds before >>>> y2038 deadline. >>> >>> Since it's all unsigned arithmetic, it should be fine until 2106. >>> However, we should get rid of get_seconds() long before then >>> and use ktime_get_real_seconds() instead, as most other users >>> of get_seconds() are (more) broken. >> >> Dtime on disk representation again breaks this for certain values in >> 2038 even though everything is unsigned. >> >> I was just saying that whatever we do here depends on how dtime on >> disk is interpreted. >> >> Agree that ktime_get_real_seconds() should be used here. But, the way >> we handle new values would rely on this new interpretation of dtime. >> Also, using time64_t variables on stack only matters after this. Once >> the types are corrected, maybe the comparison expression need not >> change at all (after new dtime interpretation is in place). > > There will not be a new dtime format on disk, but since the calculation > here only depends on relative times (within a few minutes), then it would > be fine to use only 32-bit timestamps, and truncate off the high bits > from get_seconds()/ktime_get_real_seconds(). Agreed. Are you planning to apply your fix for it then? I think your first suggestion is all we need, aside from the three minor comments I had. Arnd