From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Mason Subject: Re: [RFC v2] block integrity: Stabilize(?) pages during writeback Date: Tue, 26 Apr 2011 07:33:18 -0400 Message-ID: <1303817010-sup-351@think> References: <20110407165700.GB7363@quack.suse.cz> <20110408203135.GH1110@tux1.beaverton.ibm.com> <20110411124229.47bc28f6@corrin.poochiereds.net> <1302543595-sup-4352@think> <1302569212.2580.13.camel@mingming-laptop> <20110412005719.GA23077@infradead.org> <1302742128.2586.274.camel@mingming-laptop> <20110422000226.GA22189@tux1.beaverton.ibm.com> <1303476503-sup-4141@think> <20110422203434.GA2977@quack.suse.cz> <20110426003738.GB22189@tux1.beaverton.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Cc: Jan Kara , Mingming Cao , Christoph Hellwig , Jeff Layton , Dave Chinner , Joel Becker , "Martin K. Petersen" , Jens Axboe , linux-kernel , linux-fsdevel , Mingming Cao , linux-scsi , Dave Hansen To: djwong Return-path: In-reply-to: <20110426003738.GB22189@tux1.beaverton.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Excerpts from Darrick J. Wong's message of 2011-04-25 20:37:38 -0400: > On Fri, Apr 22, 2011 at 10:34:34PM +0200, Jan Kara wrote: > > On Fri 22-04-11 08:50:01, Chris Mason wrote: > > > Excerpts from Darrick J. Wong's message of 2011-04-21 20:02:26 -0400: > > > > Hi everyone, > > > > > > > > I've finally managed to get together a patch that seems to provide stable pages > > > > during writeback, or at least gets us to the point that after several days of > > > > running tests I don't see DIF checksum errors anymore. :) > > > > > > > > The last two pieces to go into this puzzle were (a) bio_integrity_prep needs to > > > > walk the process tree to find all userland ptes that map to a particular memory > > > > page and revoke write access, and > > > > > > Hmm, did you need the bio_integrity_prep change for all the filesystems? > > > This should be happening already as part of using page_mkwrite. > > Or more precisely page_mkclean() should do what you try to do in > > bio_integrity_prep()... It would certainly be interesting (bug) if you > > could write to the page after calling page_mkclean() without page_mkwrite() > > being called. > > Hm... in mpage_da_submit_io I see the following sequence of calls: > > 1. clear_page_dirty_for_io > 2. possibly one of: ext4_bio_write_page or block_write_full_page. > If ext4_bio_write_page, > 2a. kmem_cache_alloc > 2b. set_page_writeback > > Before and after #1, the page is locked but writeback is not set. > > Before #2, the page must be locked and writeback must not be set, because both > of those two functions want to set the writeback bit themselves. However, > ext4_bio_write_page tries to allocate memory with GFP_NOFS, which means it can > sleep (I think). Sleeping isn't the problem as long as you sleep with the page locked. The idea is that writepage will: 1) lock the page 2) clear_page_dirty_for_io (which calls page_mkclean) 3) set_page_writeback() 4) unlock the page 5) start the IO page_mkwrite will: 1) lock the page 2) wait on page writeback 3) do other stuff So if ext is calling set_page_writeback() on an unlocked page, that's a problem. Otherwise it should be working. -chris