From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx183.postini.com [74.125.245.183]) by kanga.kvack.org (Postfix) with SMTP id 898DB6B015F for ; Wed, 1 May 2013 03:38:18 -0400 (EDT) Received: by mail-ia0-f176.google.com with SMTP id l27so1162063iae.21 for ; Wed, 01 May 2013 00:38:17 -0700 (PDT) Message-ID: <5180C663.7080803@gmail.com> Date: Wed, 01 May 2013 15:38:11 +0800 From: Will Huck MIME-Version: 1.0 Subject: Re: [PATCH] swap: redirty page if page write fails on swap file References: <516E918B.3050309@redhat.com> <20130422133746.ffbbb70c0394fdbf1096c7ee@linux-foundation.org> <5177AC75.7090101@redhat.com> In-Reply-To: <5177AC75.7090101@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Marchand Cc: Andrew Morton , "linux-mm@kvack.org" , linux-kernel , Mel Gorman , Hugh Dickins Hi Jerome, On 04/24/2013 05:57 PM, Jerome Marchand wrote: > 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). After set AS_EIO or AS_ENOSPC, we can't touch swapper_space any more, correct? > >> 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, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org