Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758129Ab3DXJ5i (ORCPT ); Wed, 24 Apr 2013 05:57:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:16709 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757677Ab3DXJ5h (ORCPT ); Wed, 24 Apr 2013 05:57:37 -0400 Message-ID: <5177AC75.7090101@redhat.com> Date: Wed, 24 Apr 2013 11:57:09 +0200 From: Jerome Marchand User-Agent: Mozilla/5.0 (X11; Linux i686; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 MIME-Version: 1.0 To: Andrew Morton CC: "linux-mm@kvack.org" , linux-kernel , Mel Gorman , Hugh Dickins Subject: Re: [PATCH] swap: redirty page if page write fails on swap file References: <516E918B.3050309@redhat.com> <20130422133746.ffbbb70c0394fdbf1096c7ee@linux-foundation.org> In-Reply-To: <20130422133746.ffbbb70c0394fdbf1096c7ee@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1998 Lines: 59 On 04/22/2013 10:37 PM, Andrew Morton wrote: > On Wed, 17 Apr 2013 14:11:55 +0200 Jerome Marchand wrote: > >> >> Since commit 62c230b, swap_writepage() calls direct_IO on swap files. >> However, in that case page isn't redirtied if I/O fails, and is therefore >> handled afterwards as if it has been successfully written to the swap >> file, leading to memory corruption when the page is eventually swapped >> back in. >> This patch sets the page dirty when direct_IO() fails. It fixes a memory >> corruption that happened while using swap-over-NFS. >> >> ... >> >> --- a/mm/page_io.c >> +++ b/mm/page_io.c >> @@ -222,6 +222,8 @@ int swap_writepage(struct page *page, struct writeback_control *wbc) >> if (ret == PAGE_SIZE) { >> count_vm_event(PSWPOUT); >> ret = 0; >> + } else { >> + set_page_dirty(page); >> } >> return ret; >> } > > So what happens to the page now? It remains dirty and the kernel later > tries to write it again? Yes. Also, AS_EIO or AS_ENOSPC is set to the address space flags (in this case, swapper_space). > And if that write also fails, the page is > effectively leaked until process exit? AFAICT, there is no special handling for that page afterwards, so if all subsequent attempts fail, it's indeed going to stay in memory until freed. Jerome > > > Aside: Mel, __swap_writepage() is fairly hair-raising. It unlocks the > page before doing the IO and doesn't set PageWriteback(). Why such an > exception from normal handling? > > Also, what is protecting the page from concurrent reclaim or exit() > during the above swap_writepage()? > > Seems that the code needs a bunch of fixes or a bunch of comments > explaining why it is safe and why it has to be this way. > -- 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/