From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f42.google.com (mail-yh0-f42.google.com [209.85.213.42]) by kanga.kvack.org (Postfix) with ESMTP id 0C3726B0035 for ; Sun, 12 Jan 2014 22:51:44 -0500 (EST) Received: by mail-yh0-f42.google.com with SMTP id z6so2111826yhz.1 for ; Sun, 12 Jan 2014 19:51:43 -0800 (PST) Received: from mail-ig0-x231.google.com (mail-ig0-x231.google.com [2607:f8b0:4001:c05::231]) by mx.google.com with ESMTPS id o28si18762910yhd.266.2014.01.12.19.51.42 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Sun, 12 Jan 2014 19:51:43 -0800 (PST) Received: by mail-ig0-f177.google.com with SMTP id k19so1730964igc.4 for ; Sun, 12 Jan 2014 19:51:42 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20140112192744.9bca5c6d.akpm@linux-foundation.org> References: <000001cf0cfd$6d251640$476f42c0$%yang@samsung.com> <20140110171108.32b2be171cd5e54bf22fb2a4@linux-foundation.org> <20140112192744.9bca5c6d.akpm@linux-foundation.org> Date: Mon, 13 Jan 2014 11:51:42 +0800 Message-ID: Subject: Re: [PATCH] mm/swap: fix race on swap_info reuse between swapoff and swapon From: Weijie Yang Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Weijie Yang , linux-kernel , Linux-MM , Hugh Dickins , Minchan Kim , Shaohua Li , Bob Liu , stable@vger.kernel.org, Krzysztof Kozlowski On Mon, Jan 13, 2014 at 11:27 AM, Andrew Morton wrote: > On Mon, 13 Jan 2014 11:08:58 +0800 Weijie Yang wrote: > >> >> --- a/mm/swapfile.c >> >> +++ b/mm/swapfile.c >> >> @@ -1922,7 +1922,6 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> >> p->swap_map = NULL; >> >> cluster_info = p->cluster_info; >> >> p->cluster_info = NULL; >> >> - p->flags = 0; >> >> frontswap_map = frontswap_map_get(p); >> >> spin_unlock(&p->lock); >> >> spin_unlock(&swap_lock); >> >> @@ -1948,6 +1947,16 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile) >> >> mutex_unlock(&inode->i_mutex); >> >> } >> >> filp_close(swap_file, NULL); >> >> + >> >> + /* >> >> + * clear SWP_USED flag after all resources freed >> >> + * so that swapon can reuse this swap_info in alloc_swap_info() safely >> >> + * it is ok to not hold p->lock after we cleared its SWP_WRITEOK >> >> + */ >> >> + spin_lock(&swap_lock); >> >> + p->flags = 0; >> >> + spin_unlock(&swap_lock); >> >> + >> >> err = 0; >> >> atomic_inc(&proc_poll_event); >> >> wake_up_interruptible(&proc_poll_wait); >> > >> > I didn't look too closely, but this patch might also address the race >> > which Krzysztof addressed with >> > http://ozlabs.org/~akpm/mmots/broken-out/swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch. >> > Can we please check that out? >> > >> > I do prefer fixing all these swapon-vs-swapoff races with some large, >> > simple, wide-scope exclusion scheme. Perhaps SWP_USED is that scheme. >> > >> > An alternative would be to add another mutex and just make sys_swapon() >> > and sys_swapoff() 100% exclusive. But that is plastering yet another >> > lock over this mess to hide the horrors which lurk within :( >> > >> >> Hi, Andrew. Thanks for your suggestion. >> >> I checked Krzysztof's patch, it use the global swapon_mutex to protect >> race condition among >> swapon, swapoff and swap_start(). It is a kind of correct method, but >> a heavy method. > > But do you agree that your > http://ozlabs.org/~akpm/mmots/broken-out/mm-swap-fix-race-on-swap_info-reuse-between-swapoff-and-swapon.patch > makes Krzysztof's > http://ozlabs.org/~akpm/mmots/broken-out/swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch > obsolete? Yes, I agree. > I've been sitting on Krzysztof's > swap-fix-setting-page_size-blocksize-during-swapoff-swapon-race.patch > for several months - Hugh had issues with it so I put it on hold and > nothing further happened. > >> I will try to resend a patchset to make lock usage in swapfile.c clear >> and fine grit > > OK, thanks. In the meanwhile I'm planning on dropping Krzysztof's > patch and merging your patch into 3.14-rc1, which is why I'd like > confirmation that your patch addresses the issues which Krzysztof > identified? > I think so, Krzysztof and I both try to fix the same issue(reuse swap_info while its previous resources are not cleared completely). The different is Krzysztof's patch uses a global swapon_mutex and its commit log only focuses on set_blocksize(), while my patch try to maintain the fine grit lock usage. -- 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