From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from relay.sgi.com (relay1.corp.sgi.com [137.38.102.111]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id mB555w5h013188 for ; Thu, 4 Dec 2008 23:05:58 -0600 Message-ID: <4938B6CA.80205@sgi.com> Date: Fri, 05 Dec 2008 16:06:18 +1100 From: Lachlan McIlroy MIME-Version: 1.0 Subject: Re: [PATCH] Fix off by one error in page_region_mask() References: <49378B60.1060603@sgi.com> <4937FAED.7060503@sandeen.net> <49387CDE.2030904@sgi.com> <4938B3B4.6080505@sandeen.net> In-Reply-To: <4938B3B4.6080505@sandeen.net> Reply-To: lachlan@sgi.com List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: xfs-oss Eric Sandeen wrote: > Lachlan McIlroy wrote: >> Eric Sandeen wrote: >>> Lachlan McIlroy wrote: >>>> final is calculated to be the last bit to set (ie inclusive) but when we >>>> do the mask shifting final really needs to be first bit not to set. >>>> >>>> For example if first and final are both bit 0 (ie only first bit to be set) >>>> then mask is completely shifted and becomes all zeroes. >>>> >>>> Or if first is 0 and final is 63 then the mask is shifted one bit when it >>>> shouldn't be shifted at all. >>> Lachlan, what's the end result of this bug? What's the broken behavior? >> There was no observed bug - well nothing I can tie directly to this code. >> I found this by inspection while investigating the page bitmap stuff. >> We have a problem with ia64 going to 64K page size with filesystems that >> use a filesystem sector size of 512 bytes - we don't have the granularity >> we need in the bitmap. >> >> I suppose it is possible this bug could indicate a page region is not up >> to date when it actually is and we might re-read something from disk and >> overwrite the more up to date in-memory version. > > ah, ok. So I've seen this corruption on 64k pages too, on ppc... but I > take it this patch doesn't fix it... I don't know - it might help. But there's still an issue beyond this patch that needs fixing. _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs