Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756865Ab2J1Xtf (ORCPT ); Sun, 28 Oct 2012 19:49:35 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41795 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755668Ab2J1X1B (ORCPT ); Sun, 28 Oct 2012 19:27:01 -0400 Message-Id: <20121028231606.216765974@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Sun, 28 Oct 2012 23:17:10 +0000 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Jan Kara , Martin Schwidefsky , Mel Gorman , Hugh Dickins , Heiko Carstens , Linus Torvalds Subject: [ 094/105] mm: fix XFS oops due to dirty pages without buffers on s390 In-Reply-To: <20121028231536.970033833@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4343 Lines: 112 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Kara commit ef5d437f71afdf4afdbab99213add99f4b1318fd upstream. On s390 any write to a page (even from kernel itself) sets architecture specific page dirty bit. Thus when a page is written to via buffered write, HW dirty bit gets set and when we later map and unmap the page, page_remove_rmap() finds the dirty bit and calls set_page_dirty(). Dirtying of a page which shouldn't be dirty can cause all sorts of problems to filesystems. The bug we observed in practice is that buffers from the page get freed, so when the page gets later marked as dirty and writeback writes it, XFS crashes due to an assertion BUG_ON(!PagePrivate(page)) in page_buffers() called from xfs_count_page_state(). Similar problem can also happen when zero_user_segment() call from xfs_vm_writepage() (or block_write_full_page() for that matter) set the hardware dirty bit during writeback, later buffers get freed, and then page unmapped. Fix the issue by ignoring s390 HW dirty bit for page cache pages of mappings with mapping_cap_account_dirty(). This is safe because for such mappings when a page gets marked as writeable in PTE it is also marked dirty in do_wp_page() or do_page_fault(). When the dirty bit is cleared by clear_page_dirty_for_io(), the page gets writeprotected in page_mkclean(). So pagecache page is writeable if and only if it is dirty. Thanks to Hugh Dickins for pointing out mapping has to have mapping_cap_account_dirty() for things to work and proposing a cleaned up variant of the patch. The patch has survived about two hours of running fsx-linux on tmpfs while heavily swapping and several days of running on out build machines where the original problem was triggered. Signed-off-by: Jan Kara Cc: Martin Schwidefsky Cc: Mel Gorman Cc: Hugh Dickins Cc: Heiko Carstens Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [bwh: Backported to 3.2: adjust context; in particular there is no local 'anon' in page_remove_rmap()] Signed-off-by: Ben Hutchings --- --- a/mm/rmap.c +++ b/mm/rmap.c @@ -56,6 +56,7 @@ #include #include #include +#include #include @@ -935,11 +936,8 @@ int page_mkclean(struct page *page) if (page_mapped(page)) { struct address_space *mapping = page_mapping(page); - if (mapping) { + if (mapping) ret = page_mkclean_file(mapping, page); - if (page_test_and_clear_dirty(page_to_pfn(page), 1)) - ret = 1; - } } return ret; @@ -1120,6 +1118,8 @@ void page_add_file_rmap(struct page *pag */ void page_remove_rmap(struct page *page) { + struct address_space *mapping = page_mapping(page); + /* page still mapped by someone else? */ if (!atomic_add_negative(-1, &page->_mapcount)) return; @@ -1130,8 +1130,19 @@ void page_remove_rmap(struct page *page) * this if the page is anon, so about to be freed; but perhaps * not if it's in swapcache - there might be another pte slot * containing the swap entry, but page not yet written to swap. + * + * And we can skip it on file pages, so long as the filesystem + * participates in dirty tracking; but need to catch shm and tmpfs + * and ramfs pages which have been modified since creation by read + * fault. + * + * Note that mapping must be decided above, before decrementing + * mapcount (which luckily provides a barrier): once page is unmapped, + * it could be truncated and page->mapping reset to NULL at any moment. + * Note also that we are relying on page_mapping(page) to set mapping + * to &swapper_space when PageSwapCache(page). */ - if ((!PageAnon(page) || PageSwapCache(page)) && + if (mapping && !mapping_cap_account_dirty(mapping) && page_test_and_clear_dirty(page_to_pfn(page), 1)) set_page_dirty(page); /* -- 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/