From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: Wrong DIF guard tag on ext2 write Date: Tue, 1 Jun 2010 15:35:28 -0400 Message-ID: <20100601193528.GV8980@think> References: <20100601103041.GA15922@schmichrtp.mainz.de.ibm.com> <1275398876.21962.6.camel@mulgrave.site> <20100601133341.GK8980@think> <1275399637.21962.11.camel@mulgrave.site> <20100601134951.GM8980@think> <20100601162929.GC32708@parisc-linux.org> <20100601164750.GQ8980@think> <1275411293.21962.387.camel@mulgrave.site> <20100601180905.GR8980@think> <20100601184649.GE9453@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: James Bottomley , Matthew Wilcox , Christof Schmitt , Boaz Harrosh , "Martin K. Petersen" , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Nick Piggin Return-path: Content-Disposition: inline In-Reply-To: <20100601184649.GE9453@laptop> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, Jun 02, 2010 at 04:46:49AM +1000, Nick Piggin wrote: > On Tue, Jun 01, 2010 at 02:09:05PM -0400, Chris Mason wrote: > > On Tue, Jun 01, 2010 at 04:54:53PM +0000, James Bottomley wrote: > > > > > For self > > > induced errors (as long as we can detect them) I think we can just > > > forget about it ... if the changed page is important, the I/O request > > > gets repeated (modulo the problem of too great a frequency of changes > > > leading to us never successfully writing it) or it gets dropped because > > > the file was truncated or the data deleted for some other reason. > > > > Sorry, how can we tell the errors that are self induced from the evil > > bit flipping cable induced errors? > > Block layer should retry it with bounce pages. That would be a lot nicer > than forcing all upper layers to avoid the problem. > So the idea is that we have sent down a buffer and it changed in flight. The block layer is going to say: oh look, the crcs don't match, I'll bounce it, recrc it and send again. But, there are at least 3 reasons the crc will change: 1) filesystem changed it 2) corruption on the wire or in the raid controller 3) the page was corrupted while the IO layer was doing the IO. 1 and 2 are easy, we bounce, retry and everyone continues on with their lives. With #3, we'll recrc and send the IO down again thinking the data is correct when really we're writing garbage. How can we tell these three cases apart? -chris