Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756702AbYAOTaf (ORCPT ); Tue, 15 Jan 2008 14:30:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751613AbYAOTaZ (ORCPT ); Tue, 15 Jan 2008 14:30:25 -0500 Received: from viefep18-int.chello.at ([213.46.255.22]:58697 "EHLO viefep15-int.chello.at" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751668AbYAOTaY (ORCPT ); Tue, 15 Jan 2008 14:30:24 -0500 Subject: Re: [PATCH 2/2] Updating ctime and mtime at syncing From: Peter Zijlstra To: Anton Salikhmetov Cc: linux-mm@kvack.org, jakob@unthought.net, linux-kernel@vger.kernel.org, valdis.kletnieks@vt.edu, riel@redhat.com, ksm@42.dk, staubach@redhat.com, jesper.juhl@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, protasnb@gmail.com, miklos@szeredi.hu In-Reply-To: <4df4ef0c0801150918l71504c81s49fc8c9e427896f3@mail.gmail.com> References: <12004129652397-git-send-email-salikhmetov@gmail.com> <1200412978699-git-send-email-salikhmetov@gmail.com> <1200414911.26045.32.camel@twins> <4df4ef0c0801150918l71504c81s49fc8c9e427896f3@mail.gmail.com> Content-Type: text/plain Date: Tue, 15 Jan 2008 20:30:20 +0100 Message-Id: <1200425420.26045.42.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.21.5 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3921 Lines: 87 On Tue, 2008-01-15 at 20:18 +0300, Anton Salikhmetov wrote: > 2008/1/15, Peter Zijlstra : > > > > On Tue, 2008-01-15 at 19:02 +0300, Anton Salikhmetov wrote: > > > > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > > index 3d3848f..53d0e34 100644 > > > --- a/mm/page-writeback.c > > > +++ b/mm/page-writeback.c > > > @@ -997,35 +997,39 @@ int __set_page_dirty_no_writeback(struct page *page) > > > */ > > > int __set_page_dirty_nobuffers(struct page *page) > > > { > > > - if (!TestSetPageDirty(page)) { > > > - struct address_space *mapping = page_mapping(page); > > > - struct address_space *mapping2; > > > + struct address_space *mapping = page_mapping(page); > > > + struct address_space *mapping2; > > > > > > - if (!mapping) > > > - return 1; > > > + if (!mapping) > > > + return 1; > > > > > > - write_lock_irq(&mapping->tree_lock); > > > - mapping2 = page_mapping(page); > > > - if (mapping2) { /* Race with truncate? */ > > > - BUG_ON(mapping2 != mapping); > > > - WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); > > > - if (mapping_cap_account_dirty(mapping)) { > > > - __inc_zone_page_state(page, NR_FILE_DIRTY); > > > - __inc_bdi_stat(mapping->backing_dev_info, > > > - BDI_RECLAIMABLE); > > > - task_io_account_write(PAGE_CACHE_SIZE); > > > - } > > > - radix_tree_tag_set(&mapping->page_tree, > > > - page_index(page), PAGECACHE_TAG_DIRTY); > > > - } > > > - write_unlock_irq(&mapping->tree_lock); > > > - if (mapping->host) { > > > - /* !PageAnon && !swapper_space */ > > > - __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); > > > + mapping->mtime = CURRENT_TIME; > > > + set_bit(AS_MCTIME, &mapping->flags); > > > > This seems vulnerable to the race we have against truncate, handled by > > the mapping2 magic below. Do we care? > > > > > + > > > + if (TestSetPageDirty(page)) > > > + return 0; > > > + > > > + write_lock_irq(&mapping->tree_lock); > > > + mapping2 = page_mapping(page); > > > + if (mapping2) { > > > + /* Race with truncate? */ > > > + BUG_ON(mapping2 != mapping); > > > + WARN_ON_ONCE(!PagePrivate(page) && !PageUptodate(page)); > > > + if (mapping_cap_account_dirty(mapping)) { > > > + __inc_zone_page_state(page, NR_FILE_DIRTY); > > > + __inc_bdi_stat(mapping->backing_dev_info, > > > + BDI_RECLAIMABLE); > > > + task_io_account_write(PAGE_CACHE_SIZE); > > > } > > > - return 1; > > > + radix_tree_tag_set(&mapping->page_tree, > > > + page_index(page), PAGECACHE_TAG_DIRTY); > > > } > > > - return 0; > > > + write_unlock_irq(&mapping->tree_lock); > > > + > > > + if (mapping->host) > > > + __mark_inode_dirty(mapping->host, I_DIRTY_PAGES); > > The inode gets marked dirty using the same "mapping" variable > as my code does. So, AFAIU, my change does not introduce any new > vulnerabilities. I would nevertherless be grateful to you for a scenario > where the race would be triggered. Ah, right, so that would be a resounding no to my previous question :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/