From patchwork Wed Mar 23 13:49:39 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Xiaoguang Wang X-Patchwork-Id: 553845 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88BC5C4167D for ; Wed, 23 Mar 2022 13:49:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244519AbiCWNvR (ORCPT ); Wed, 23 Mar 2022 09:51:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244508AbiCWNvP (ORCPT ); Wed, 23 Mar 2022 09:51:15 -0400 Received: from out30-43.freemail.mail.aliyun.com (out30-43.freemail.mail.aliyun.com [115.124.30.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 590984706A; Wed, 23 Mar 2022 06:49:45 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R961e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=e01e04400; MF=xiaoguang.wang@linux.alibaba.com; NM=1; PH=DS; RN=4; SR=0; TI=SMTPD_---0V80FjZU_1648043382; Received: from localhost(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0V80FjZU_1648043382) by smtp.aliyun-inc.com(127.0.0.1); Wed, 23 Mar 2022 21:49:43 +0800 From: Xiaoguang Wang To: linux-scsi@vger.kernel.org, target-devel@vger.kernel.org Cc: linux-block@vger.kernel.org, bostroesser@gmail.com Subject: [PATCH v2 2/3] scsi: target: tcmu: Fix possible data corruption Date: Wed, 23 Mar 2022 21:49:39 +0800 Message-Id: <20220323134940.31463-3-xiaoguang.wang@linux.alibaba.com> X-Mailer: git-send-email 2.17.2 In-Reply-To: <20220323134940.31463-1-xiaoguang.wang@linux.alibaba.com> References: <20220323134940.31463-1-xiaoguang.wang@linux.alibaba.com> Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org When tcmu_vma_fault() gets one page successfully, before the current context completes page fault procedure, find_free_blocks() may run in and call unmap_mapping_range() to unmap this page. Assume when find_free_blocks() completes its job firstly, previous page fault procedure starts to run again and completes, then one truncated page has beed mapped to use space, but note that tcmu_vma_fault() has gotten one refcount for this page, so any other subsystem won't use this page, unless later the use space addr is unmapped. If another command runs in later and needs to extends dbi_thresh, it may reuse the corresponding slot to previous page in data_bitmap, then thouth we'll allocate new page for this slot in data_area, but no page fault will happen again, because we have a valid map, real request's data will lose. To fix this issue, when extending dbi_thresh, we'll need to call unmap_mapping_range() to unmap use space data area which may exist, which I think it's a simple method. Filesystem implementations will also run into this issue, but they ususally lock page when vm_operations_struct->fault gets one page, and unlock page after finish_fault() completes. In truncate sides, they lock pages in truncate_inode_pages() to protect race with page fault. We can also have similar codes like filesystem to fix this issue. Signed-off-by: Xiaoguang Wang --- drivers/target/target_core_user.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c index 06a5c4086551..9196188504ec 100644 --- a/drivers/target/target_core_user.c +++ b/drivers/target/target_core_user.c @@ -862,6 +862,7 @@ static int tcmu_alloc_data_space(struct tcmu_dev *udev, struct tcmu_cmd *cmd, if (space < cmd->dbi_cnt) { unsigned long blocks_left = (udev->max_blocks - udev->dbi_thresh) + space; + loff_t off, len; if (blocks_left < cmd->dbi_cnt) { pr_debug("no data space: only %lu available, but ask for %u\n", @@ -870,6 +871,10 @@ static int tcmu_alloc_data_space(struct tcmu_dev *udev, struct tcmu_cmd *cmd, return -1; } + off = udev->data_off + (loff_t)udev->dbi_thresh * udev->data_blk_size; + len = cmd->dbi_cnt * udev->data_blk_size; + unmap_mapping_range(udev->inode->i_mapping, off, len, 1); + udev->dbi_thresh += cmd->dbi_cnt; if (udev->dbi_thresh > udev->max_blocks) udev->dbi_thresh = udev->max_blocks;