From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA30EC433F5 for ; Mon, 23 May 2022 03:01:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id EB5AD6B0005; Sun, 22 May 2022 23:01:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E65826B0006; Sun, 22 May 2022 23:01:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D7B0D6B0007; Sun, 22 May 2022 23:01:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id CA5A76B0005 for ; Sun, 22 May 2022 23:01:20 -0400 (EDT) Received: from smtpin09.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 9256234AAA for ; Mon, 23 May 2022 03:01:20 +0000 (UTC) X-FDA: 79495506720.09.E608A6D Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf12.hostedemail.com (Postfix) with ESMTP id 0E6804001D for ; Mon, 23 May 2022 03:00:45 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4L62Bp5ZZPzhYYw; Mon, 23 May 2022 11:00:34 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 23 May 2022 11:01:14 +0800 Subject: Re: [PATCH v4 4/5] mm/shmem: fix infinite loop when swap in shmem error at swapoff time To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: "akpm@linux-foundation.org" , "hughd@google.com" , "willy@infradead.org" , "vbabka@suse.cz" , "dhowells@redhat.com" , "neilb@suse.de" , "apopple@nvidia.com" , "david@redhat.com" , "surenb@google.com" , "peterx@redhat.com" , "rcampbell@nvidia.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20220519125030.21486-1-linmiaohe@huawei.com> <20220519125030.21486-5-linmiaohe@huawei.com> <20220520063433.GA584983@hori.linux.bs1.fc.nec.co.jp> <970aee34-c377-2b8c-c6bb-45e2a96e84b9@huawei.com> <20220522235326.GA713751@hori.linux.bs1.fc.nec.co.jp> From: Miaohe Lin Message-ID: <7269c0c4-7648-a9dc-10fa-3645da5be441@huawei.com> Date: Mon, 23 May 2022 11:01:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20220522235326.GA713751@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Rspam-User: X-Rspamd-Queue-Id: 0E6804001D X-Stat-Signature: wi91iy9abpxorphnp7ojw9dgbbcu33jk Authentication-Results: imf12.hostedemail.com; dkim=none; spf=pass (imf12.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspamd-Server: rspam03 X-HE-Tag: 1653274845-459377 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2022/5/23 7:53, HORIGUCHI NAOYA(堀口 直也) wrote: > On Fri, May 20, 2022 at 04:17:45PM +0800, Miaohe Lin wrote: >> On 2022/5/20 14:34, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Thu, May 19, 2022 at 08:50:29PM +0800, Miaohe Lin wrote: >>>> When swap in shmem error at swapoff time, there would be a infinite loop >>>> in the while loop in shmem_unuse_inode(). It's because swapin error is >>>> deliberately ignored now and thus info->swapped will never reach 0. So >>>> we can't escape the loop in shmem_unuse(). >>>> >>>> In order to fix the issue, swapin_error entry is stored in the mapping >>>> when swapin error occurs. So the swapcache page can be freed and the >>>> user won't end up with a permanently mounted swap because a sector is >>>> bad. If the page is accessed later, the user process will be killed >>>> so that corrupted data is never consumed. On the other hand, if the >>>> page is never accessed, the user won't even notice it. >>>> >>>> Reported-by: Naoya Horiguchi >>>> Signed-off-by: Miaohe Lin >>> >>> Hi Miaohe, >>> >>> Thank you for the update. I might miss something, but I still see the same >>> problem (I checked it on mm-everything-2022-05-19-00-03 + this patchset). >> >> I was testing this patch on my 5.10 kernel. I reproduced the problem in my env and >> fixed it. It seems there might be some critical difference though I checked that by >> reviewing the code... Sorry. :( >> >>> >>> This patch has the effect to change the return value of shmem_swapin_folio(), >>> -EIO (without this patch) to -EEXIST (with this patch). >> >> In fact, I didn't change the return value from -EIO to -EEXIST: >> >> @@ -1762,6 +1799,8 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index, >> failed: >> if (!shmem_confirm_swap(mapping, index, swap)) >> error = -EEXIST; >> + if (error == -EIO) >> + shmem_set_folio_swapin_error(inode, index, folio, swap) >> >>> But shmem_unuse_swap_entries() checks neither, so no change from caller's view point. >>> Maybe breaking in errors (rather than ENOMEM) in for loop in shmem_unuse_swap_entries() >>> solves the issue? I briefly checked with the below change, then swapoff can return >>> with failure. >>> >>> @@ -1222,7 +1222,7 @@ static int shmem_unuse_swap_entries(struct inode *inode, >>> folio_put(folio); >>> ret++; >>> } >>> - if (error == -ENOMEM) >>> + if (error < 0) >>> break; >>> error = 0; >>> } >> >> Yes, this is the simplest and straightforward way to fix the issue. But it has the side effect >> that user will end up with a permanently mounted swap just because a sector is bad. That might >> be somewhat unacceptable? > > Ah, you're right, swapoff should return with success instead of with > failure. I tried the fix in your another email, and that makes swapoff > return with success, so your fix looks better than mine. I reproduced the deadloop issues when swapin error occurs at swapoff time in my linux-next-next-20220520 env, and I found this patch could solve the issue now with the fix in my another email. BTW: When I use dm-dust to inject the swapin IO error, I don't see non-uptodate folio when shmem_swapin_folio and swapoff succeeds. There might be some issues around that module (so I resort to the another way to inject the swapin error), but the patch itself works anyway. ;) > > Thanks, Thanks a lot! > Naoya Horiguchi >