Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932939AbaLBL5K (ORCPT ); Tue, 2 Dec 2014 06:57:10 -0500 Received: from mta-out1.inet.fi ([62.71.2.203]:32946 "EHLO kirsi1.inet.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753796AbaLBL5I (ORCPT ); Tue, 2 Dec 2014 06:57:08 -0500 Date: Tue, 2 Dec 2014 13:56:52 +0200 From: "Kirill A. Shutemov" To: Johannes Weiner Cc: Andrew Morton , Tejun Heo , Hugh Dickins , Michel Lespinasse , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 1/3] mm: protect set_page_dirty() from ongoing truncation Message-ID: <20141202115652.GB22683@node.dhcp.inet.fi> References: <1417474682-29326-1-git-send-email-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1417474682-29326-1-git-send-email-hannes@cmpxchg.org> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 01, 2014 at 05:58:00PM -0500, Johannes Weiner wrote: > Tejun, while reviewing the code, spotted the following race condition > between the dirtying and truncation of a page: > > __set_page_dirty_nobuffers() __delete_from_page_cache() > if (TestSetPageDirty(page)) > page->mapping = NULL > if (PageDirty()) > dec_zone_page_state(page, NR_FILE_DIRTY); > dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > if (page->mapping) > account_page_dirtied(page) > __inc_zone_page_state(page, NR_FILE_DIRTY); > __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > > which results in an imbalance of NR_FILE_DIRTY and BDI_RECLAIMABLE. > > Dirtiers usually lock out truncation, either by holding the page lock > directly, or in case of zap_pte_range(), by pinning the mapcount with > the page table lock held. The notable exception to this rule, though, > is do_wp_page(), for which this race exists. However, do_wp_page() > already waits for a locked page to unlock before setting the dirty > bit, in order to prevent a race where clear_page_dirty() misses the > page bit in the presence of dirty ptes. Upgrade that wait to a fully > locked set_page_dirty() to also cover the situation explained above. > > Afterwards, the code in set_page_dirty() dealing with a truncation > race is no longer needed. Remove it. > > Reported-by: Tejun Heo > Signed-off-by: Johannes Weiner > Cc: > --- > include/linux/writeback.h | 1 - > mm/memory.c | 26 ++++++++++++++++---------- > mm/page-writeback.c | 43 ++++++++++++------------------------------- > 3 files changed, 28 insertions(+), 42 deletions(-) > > diff --git a/include/linux/writeback.h b/include/linux/writeback.h > index a219be961c0a..00048339c23e 100644 > --- a/include/linux/writeback.h > +++ b/include/linux/writeback.h > @@ -177,7 +177,6 @@ int write_cache_pages(struct address_space *mapping, > struct writeback_control *wbc, writepage_t writepage, > void *data); > int do_writepages(struct address_space *mapping, struct writeback_control *wbc); > -void set_page_dirty_balance(struct page *page); > void writeback_set_ratelimit(void); > void tag_pages_for_writeback(struct address_space *mapping, > pgoff_t start, pgoff_t end); > diff --git a/mm/memory.c b/mm/memory.c > index 3e503831e042..73220eb6e9e3 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2150,17 +2150,23 @@ reuse: > if (!dirty_page) > return ret; > > - /* > - * Yes, Virginia, this is actually required to prevent a race > - * with clear_page_dirty_for_io() from clearing the page dirty > - * bit after it clear all dirty ptes, but before a racing > - * do_wp_page installs a dirty pte. > - * > - * do_shared_fault is protected similarly. > - */ > if (!page_mkwrite) { > - wait_on_page_locked(dirty_page); > - set_page_dirty_balance(dirty_page); > + struct address_space *mapping; > + int dirtied; > + > + lock_page(dirty_page); > + dirtied = set_page_dirty(dirty_page); > + mapping = dirty_page->mapping; At first, I wanted to ask why you don't use page_mapping() here, but after a bit of digging I see we cannot get here with anon page. Explicid VM_BUG_ON_PAGE(PageAnon(dirty_page), dirty_page); would be great. Otherwise looks good to me. Acked-by: Kirill A. Shutemov -- Kirill A. Shutemov -- 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/