From patchwork Thu Apr 1 14:33:19 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dan Williams X-Patchwork-Id: 12188367 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9B23C433ED for ; Thu, 1 Apr 2021 17:58:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BEA5161001 for ; Thu, 1 Apr 2021 17:58:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236753AbhDAR6h (ORCPT ); Thu, 1 Apr 2021 13:58:37 -0400 Received: from mga14.intel.com ([192.55.52.115]:59020 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236893AbhDARzk (ORCPT ); Thu, 1 Apr 2021 13:55:40 -0400 IronPort-SDR: U1sJuOYSwqkoVr5A2b6V0KElHdsztjkDeQNLzO7rN5Whm30jy8/bvgdjxdZcwjlPkhk6KKiOFR 72UiJQsUtcgg== X-IronPort-AV: E=McAfee;i="6000,8403,9941"; a="191734627" X-IronPort-AV: E=Sophos;i="5.81,296,1610438400"; d="scan'208";a="191734627" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Apr 2021 07:33:22 -0700 IronPort-SDR: sElXlFcU6PLxT1vSpePXLl46lI7T8lRNPYIX4uYZJ11nwEkx9CM1dqrgkUZEBD6pdPW00Vim9U vJKXHmn155kQ== X-IronPort-AV: E=Sophos;i="5.81,296,1610438400"; d="scan'208";a="446110675" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.25]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Apr 2021 07:33:19 -0700 Subject: [PATCH v4 2/4] cxl/mem: Fix synchronization mechanism for device removal vs ioctl operations From: Dan Williams To: linux-cxl@vger.kernel.org Cc: Jason Gunthorpe , Jason Gunthorpe , linux-kernel@vger.kernel.org, vishal.l.verma@intel.com, ira.weiny@intel.com, alison.schofield@intel.com Date: Thu, 01 Apr 2021 07:33:19 -0700 Message-ID: <161728759948.2474381.17481500816783671817.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <161728758895.2474381.12683589190335430004.stgit@dwillia2-desk3.amr.corp.intel.com> References: <161728758895.2474381.12683589190335430004.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org The percpu_ref to gate whether cxl_memdev_ioctl() is free to use the driver context (@cxlm) to issue I/O is overkill, implemented incorrectly (missing a device reference before accessing the percpu_ref), and the complexities of shutting down a percpu_ref contributed to a bug in the error unwind in cxl_mem_add_memdev() (missing put_device() to be fixed separately). Use an rwsem to explicitly synchronize the usage of cxlmd->cxlm, and add the missing reference counting for cxlmd in cxl_memdev_open() and cxl_memdev_release_file(). Fixes: b39cb1052a5c ("cxl/mem: Register CXL memX devices") Reported-by: Jason Gunthorpe Reviewed-by: Jason Gunthorpe Signed-off-by: Dan Williams --- drivers/cxl/mem.c | 97 +++++++++++++++++++++++++++-------------------------- 1 file changed, 50 insertions(+), 47 deletions(-) diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c index 30bf4f0f3c17..c77d375fad95 100644 --- a/drivers/cxl/mem.c +++ b/drivers/cxl/mem.c @@ -96,21 +96,18 @@ struct mbox_cmd { * @dev: driver core device object * @cdev: char dev core object for ioctl operations * @cxlm: pointer to the parent device driver data - * @ops_active: active user of @cxlm in ops handlers - * @ops_dead: completion when all @cxlm ops users have exited * @id: id number of this memdev instance. */ struct cxl_memdev { struct device dev; struct cdev cdev; struct cxl_mem *cxlm; - struct percpu_ref ops_active; - struct completion ops_dead; int id; }; static int cxl_mem_major; static DEFINE_IDA(cxl_memdev_ida); +static DECLARE_RWSEM(cxl_memdev_rwsem); static struct dentry *cxl_debugfs; static bool cxl_raw_allow_all; @@ -776,26 +773,43 @@ static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd, static long cxl_memdev_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { - struct cxl_memdev *cxlmd; - struct inode *inode; - int rc = -ENOTTY; + struct cxl_memdev *cxlmd = file->private_data; + int rc = -ENXIO; - inode = file_inode(file); - cxlmd = container_of(inode->i_cdev, typeof(*cxlmd), cdev); + down_read(&cxl_memdev_rwsem); + if (cxlmd->cxlm) + rc = __cxl_memdev_ioctl(cxlmd, cmd, arg); + up_read(&cxl_memdev_rwsem); - if (!percpu_ref_tryget_live(&cxlmd->ops_active)) - return -ENXIO; + return rc; +} - rc = __cxl_memdev_ioctl(cxlmd, cmd, arg); +static int cxl_memdev_open(struct inode *inode, struct file *file) +{ + struct cxl_memdev *cxlmd = + container_of(inode->i_cdev, typeof(*cxlmd), cdev); - percpu_ref_put(&cxlmd->ops_active); + get_device(&cxlmd->dev); + file->private_data = cxlmd; - return rc; + return 0; +} + +static int cxl_memdev_release_file(struct inode *inode, struct file *file) +{ + struct cxl_memdev *cxlmd = + container_of(inode->i_cdev, typeof(*cxlmd), cdev); + + put_device(&cxlmd->dev); + + return 0; } static const struct file_operations cxl_memdev_fops = { .owner = THIS_MODULE, .unlocked_ioctl = cxl_memdev_ioctl, + .open = cxl_memdev_open, + .release = cxl_memdev_release_file, .compat_ioctl = compat_ptr_ioctl, .llseek = noop_llseek, }; @@ -1049,7 +1063,6 @@ static void cxl_memdev_release(struct device *dev) { struct cxl_memdev *cxlmd = to_cxl_memdev(dev); - percpu_ref_exit(&cxlmd->ops_active); ida_free(&cxl_memdev_ida, cxlmd->id); kfree(cxlmd); } @@ -1150,24 +1163,21 @@ static const struct device_type cxl_memdev_type = { .groups = cxl_memdev_attribute_groups, }; -static void cxlmdev_unregister(void *_cxlmd) +static void cxl_memdev_shutdown(struct cxl_memdev *cxlmd) { - struct cxl_memdev *cxlmd = _cxlmd; - struct device *dev = &cxlmd->dev; - - percpu_ref_kill(&cxlmd->ops_active); - cdev_device_del(&cxlmd->cdev, dev); - wait_for_completion(&cxlmd->ops_dead); + down_write(&cxl_memdev_rwsem); cxlmd->cxlm = NULL; - put_device(dev); + up_write(&cxl_memdev_rwsem); } -static void cxlmdev_ops_active_release(struct percpu_ref *ref) +static void cxl_memdev_unregister(void *_cxlmd) { - struct cxl_memdev *cxlmd = - container_of(ref, typeof(*cxlmd), ops_active); + struct cxl_memdev *cxlmd = _cxlmd; + struct device *dev = &cxlmd->dev; - complete(&cxlmd->ops_dead); + cdev_device_del(&cxlmd->cdev, dev); + cxl_memdev_shutdown(cxlmd); + put_device(dev); } static int cxl_mem_add_memdev(struct cxl_mem *cxlm) @@ -1181,17 +1191,6 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm) cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL); if (!cxlmd) return -ENOMEM; - init_completion(&cxlmd->ops_dead); - - /* - * @cxlm is deallocated when the driver unbinds so operations - * that are using it need to hold a live reference. - */ - cxlmd->cxlm = cxlm; - rc = percpu_ref_init(&cxlmd->ops_active, cxlmdev_ops_active_release, 0, - GFP_KERNEL); - if (rc) - goto err_ref; rc = ida_alloc_range(&cxl_memdev_ida, 0, CXL_MEM_MAX_DEVS, GFP_KERNEL); if (rc < 0) @@ -1209,23 +1208,27 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm) cdev = &cxlmd->cdev; cdev_init(cdev, &cxl_memdev_fops); + /* + * Activate ioctl operations, no cxl_memdev_rwsem manipulation + * needed as this is ordered with cdev_add() publishing the device. + */ + cxlmd->cxlm = cxlm; + rc = cdev_device_add(cdev, dev); if (rc) goto err_add; - return devm_add_action_or_reset(dev->parent, cxlmdev_unregister, cxlmd); + return devm_add_action_or_reset(dev->parent, cxl_memdev_unregister, + cxlmd); err_add: - ida_free(&cxl_memdev_ida, cxlmd->id); -err_id: /* - * Theoretically userspace could have already entered the fops, - * so flush ops_active. + * The cdev was briefly live, shutdown any ioctl operations that + * saw that state. */ - percpu_ref_kill(&cxlmd->ops_active); - wait_for_completion(&cxlmd->ops_dead); - percpu_ref_exit(&cxlmd->ops_active); -err_ref: + cxl_memdev_shutdown(cxlmd); + ida_free(&cxl_memdev_ida, cxlmd->id); +err_id: kfree(cxlmd); return rc;