From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756519Ab2C0WIc (ORCPT ); Tue, 27 Mar 2012 18:08:32 -0400 Received: from cantor2.suse.de ([195.135.220.15]:41883 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755872Ab2C0WIb (ORCPT ); Tue, 27 Mar 2012 18:08:31 -0400 Date: Wed, 28 Mar 2012 00:08:19 +0200 From: Jan Kara To: Andrew Morton Cc: Jan Kara , LKML , linux-fsdevel@vger.kernel.org, Al Viro , Christoph Hellwig , dchinner@redhat.com, sandeen@redhat.com, Kamal Mostafa Subject: Re: [PATCH 01/19] mm: Make default vm_ops provide ->page_mkwrite handler Message-ID: <20120327220819.GK5020@quack.suse.cz> References: <1330963277-26336-1-git-send-email-jack@suse.cz> <1330963277-26336-2-git-send-email-jack@suse.cz> <20120323154502.8072a755.akpm@linux-foundation.org> <20120327075527.GA5020@quack.suse.cz> <20120327143815.40456d38.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120327143815.40456d38.akpm@linux-foundation.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 27-03-12 14:38:15, Andrew Morton wrote: > On Tue, 27 Mar 2012 09:55:27 +0200 > Jan Kara wrote: > > On Fri 23-03-12 15:45:02, Andrew Morton wrote: > > > On Mon, 5 Mar 2012 17:00:59 +0100 > > > Jan Kara wrote: > > > > > > > --- a/mm/filemap.c > > > > +++ b/mm/filemap.c > > > > @@ -1759,8 +1759,28 @@ page_not_uptodate: > > > > } > > > > EXPORT_SYMBOL(filemap_fault); > > > > > > > > +int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) > > > > +{ > > > > + struct page *page = vmf->page; > > > > + struct inode *inode = vma->vm_file->f_path.dentry->d_inode; > > > > + int ret = VM_FAULT_LOCKED; > > > > + > > > > + file_update_time(vma->vm_file); > > > > + lock_page(page); > > > > + if ((page->mapping != inode->i_mapping) || > > > > + (page_offset(page) > i_size_read(inode))) { > > > > > > Would benefit from a comment explaining how the page can come to be > > > outside i_size, and why we fail in that case. > > This? > > > > I don't think i_mutex is held here, so this test is rather meaningless > > > and racy anyway? > > i_size test is racy if that's what you mean by "this test". Just I did > > the test this way because it's like this in other places and I figured > > truncate_pagecache() can take relatively long time so the test has some > > effect. But if you think it's not worth it, I can remove it. > > It bugs me when we copy-n-paste code without remembering why we had it > there in the first place :( iirc, mmapped pages outside i_size can and > do happen in some race situations, and are benign. Yeah. Certainly there can be pages beyond i_size because we first set file size and then go and remove pages beyond new i_size one by one when we do truncate. We must be careful not to create any new pages beyond i_size but that's what filemap_fault() takes care of. So I think i_size check in ->page_mkwrite() isn't strictly needed. > But it's several > years since I thought about it and all the details have evaporated and > it would take a lot of work to reinstantiate it all. argh. > > Also, it's off-by-one, isn't it? Should be page_offset(page) >= i_size? Yes, it is. I'll just remove it. Honza -- Jan Kara SUSE Labs, CR