From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755570AbcILV2a (ORCPT ); Mon, 12 Sep 2016 17:28:30 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50392 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752654AbcILV23 (ORCPT ); Mon, 12 Sep 2016 17:28:29 -0400 Date: Mon, 12 Sep 2016 14:28:27 -0700 From: Andrew Morton To: Santosh Shilimkar Cc: linux-mm@kvack.org, mgorman@suse.de, linux-kernel@vger.kernel.org, Joe Perches , Peter Zijlstra , Rik van Riel , "David S. Miller" , Jens Axboe , Michal Hocko , Hugh Dickins , Al Viro Subject: Re: [PATCH] mm: fix the page_swap_info BUG_ON check Message-Id: <20160912142827.1a20f7cdb830e44ddafd275f@linux-foundation.org> In-Reply-To: <1473460718-31013-1-git-send-email-santosh.shilimkar@oracle.com> References: <1473460718-31013-1-git-send-email-santosh.shilimkar@oracle.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 9 Sep 2016 15:38:38 -0700 Santosh Shilimkar wrote: > 'commit 62c230bc1790 ("mm: add support for a filesystem to activate swap > files and use direct_IO for writing swap pages")' replaced swap_aops > dirty hook from __set_page_dirty_no_writeback() to swap_set_page_dirty(). > As such for normal cases without these special SWP flags > code path falls back to __set_page_dirty_no_writeback() > so behaviour is expected to be same as before. > > But swap_set_page_dirty() makes use of helper page_swap_info() to > get sis(swap_info_struct) to check for the flags like SWP_FILE, > SWP_BLKDEV etc as desired for those features. This helper has > BUG_ON(!PageSwapCache(page)) which is racy and safe only for > set_page_dirty_lock() path. For set_page_dirty() path which is > often needed for cases to be called from irq context, kswapd() > can togele the flag behind the back while the call is > getting executed when system is low on memory and heavy > swapping is ongoing. > > This ends up with undesired kernel panic. Patch just moves > the check outside the helper to its users appropriately > to fix kernel panic for the described path. Couple > of users of helpers already take care of SwapCache > condition so I skipped them. > > Cc: Mel Gorman > Cc: Joe Perches > Cc: Andrew Morton > Cc: Peter Zijlstra > Cc: Rik van Riel > Cc: David S. Miller > Cc: Jens Axboe > Cc: Michal Hocko > Cc: Hugh Dickins > Cc: Al Viro I'll add Cc: [4.7.x] > --- a/mm/page_io.c > +++ b/mm/page_io.c > @@ -264,6 +264,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc, > int ret; > struct swap_info_struct *sis = page_swap_info(page); > > + BUG_ON(!PageSwapCache(page)); > if (sis->flags & SWP_FILE) { > struct kiocb kiocb; > struct file *swap_file = sis->swap_file; > @@ -337,6 +338,7 @@ int swap_readpage(struct page *page) > int ret = 0; > struct swap_info_struct *sis = page_swap_info(page); > > + BUG_ON(!PageSwapCache(page)); > VM_BUG_ON_PAGE(!PageLocked(page), page); > VM_BUG_ON_PAGE(PageUptodate(page), page); > if (frontswap_load(page) == 0) { > @@ -386,6 +388,7 @@ int swap_set_page_dirty(struct page *page) > > if (sis->flags & SWP_FILE) { > struct address_space *mapping = sis->swap_file->f_mapping; > + BUG_ON(!PageSwapCache(page)); > return mapping->a_ops->set_page_dirty(page); > } else { > return __set_page_dirty_no_writeback(page); I guess this is OK for 4.8 but for later kernels, let's quieten it down a bit? From: Andrew Morton Subject: mm/page_io.c: replace some BUG_ON()s with VM_BUG_ON_PAGE() So they are CONFIG_DEBUG_VM-only and more informative. Cc: Al Viro Cc: David S. Miller Cc: Hugh Dickins Cc: Jens Axboe Cc: Joe Perches Cc: Mel Gorman Cc: Michal Hocko Cc: Peter Zijlstra Cc: Rik van Riel Cc: Santosh Shilimkar Signed-off-by: Andrew Morton --- mm/page_io.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff -puN mm/page_io.c~mm-fix-the-page_swap_info-bug_on-check-fix mm/page_io.c --- a/mm/page_io.c~mm-fix-the-page_swap_info-bug_on-check-fix +++ a/mm/page_io.c @@ -264,7 +264,7 @@ int __swap_writepage(struct page *page, int ret; struct swap_info_struct *sis = page_swap_info(page); - BUG_ON(!PageSwapCache(page)); + VM_BUG_ON_PAGE(!PageSwapCache(page), page); if (sis->flags & SWP_FILE) { struct kiocb kiocb; struct file *swap_file = sis->swap_file; @@ -338,7 +338,7 @@ int swap_readpage(struct page *page) int ret = 0; struct swap_info_struct *sis = page_swap_info(page); - BUG_ON(!PageSwapCache(page)); + VM_BUG_ON_PAGE(!PageSwapCache(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(PageUptodate(page), page); if (frontswap_load(page) == 0) { @@ -388,7 +388,8 @@ int swap_set_page_dirty(struct page *pag if (sis->flags & SWP_FILE) { struct address_space *mapping = sis->swap_file->f_mapping; - BUG_ON(!PageSwapCache(page)); + + VM_BUG_ON_PAGE(!PageSwapCache(page), page); return mapping->a_ops->set_page_dirty(page); } else { return __set_page_dirty_no_writeback(page); diff -puN mm/swapfile.c~mm-fix-the-page_swap_info-bug_on-check-fix mm/swapfile.c _