From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from dkim2.fusionio.com ([66.114.96.54]:38493 "EHLO dkim2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756Ab3EaFMF convert rfc822-to-8bit (ORCPT ); Fri, 31 May 2013 01:12:05 -0400 Received: from mx2.fusionio.com (unknown [10.101.1.160]) by dkim2.fusionio.com (Postfix) with ESMTP id 3E5409A064D for ; Thu, 30 May 2013 23:12:04 -0600 (MDT) Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 From: Chris Mason To: Zach Brown , "linux-fsdevel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" References: <20130530223610.GA24721@lenny.home.zabbo.net> In-Reply-To: <20130530223610.GA24721@lenny.home.zabbo.net> Message-ID: <20130531051158.7927.24213@localhost.localdomain> Subject: Re: testing stable pages being modified Date: Fri, 31 May 2013 01:11:58 -0400 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Quoting Zach Brown (2013-05-30 18:36:10) > 'stable' pages have always been a bit of a fiction. It's easy to > intentionally modify stable pages under io with some help from page > references that ignore mappings and page state. > > Here's little test that uses O_DIRECT to get the pinned aio ring pages > under IO and then has event completion stores modify them while they're > in flight. > > It's a nice quick way to test the consequences of stable pages being > modified. It can be used to burp out ratelimited csum failure kernel > messages with btrfs, for example. Changing O_DIRECT in flight has always been a deep dark corner case, and crc errors are the expected result. Have you found anyone doing this in real life? I do like the small test program though, we should extend it into a test to make sure crcs are really crcing. -chris