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 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=unavailable 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 03495C433E2 for ; Tue, 30 Mar 2021 02:48:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CCD6D619BB for ; Tue, 30 Mar 2021 02:48:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231433AbhC3CsW (ORCPT ); Mon, 29 Mar 2021 22:48:22 -0400 Received: from mga09.intel.com ([134.134.136.24]:41700 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230506AbhC3Cru (ORCPT ); Mon, 29 Mar 2021 22:47:50 -0400 IronPort-SDR: OktDNNihDnMiC/D9JJGKyUXk/jFpNxB7AMXj6VUTHHLo7FGtMFhvejkZYD71NfACzD1a/dOHMW 0BtY5gPxnQEA== X-IronPort-AV: E=McAfee;i="6000,8403,9938"; a="191770679" X-IronPort-AV: E=Sophos;i="5.81,289,1610438400"; d="scan'208";a="191770679" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Mar 2021 19:47:50 -0700 IronPort-SDR: LT6Riyh3WxMBkTcK0pZPPykgNfVuCa8TxElLqTGgXvWXa6cJ4mQb5uYyshKO5kAcqf3sVo2eFj yM448i7eJUDw== X-IronPort-AV: E=Sophos;i="5.81,289,1610438400"; d="scan'208";a="444887209" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.25]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Mar 2021 19:47:49 -0700 Subject: [PATCH v2 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 , linux-kernel@vger.kernel.org, vishal.l.verma@intel.com, ira.weiny@intel.com, alison.schofield@intel.com Date: Mon, 29 Mar 2021 19:47:49 -0700 Message-ID: <161707246948.2072157.2116502455691653472.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <161707245893.2072157.6743322596719518693.stgit@dwillia2-desk3.amr.corp.intel.com> References: <161707245893.2072157.6743322596719518693.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-3-g996c MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 srcu + device_is_registered() to achieve the same effect 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 Signed-off-by: Dan Williams --- drivers/cxl/mem.c | 83 +++++++++++++++++++++++++++-------------------------- 1 file changed, 43 insertions(+), 40 deletions(-) diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c index 30bf4f0f3c17..548d696f1f54 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); +DEFINE_STATIC_SRCU(cxl_memdev_srcu); static struct dentry *cxl_debugfs; static bool cxl_raw_allow_all; @@ -763,6 +760,14 @@ static int cxl_send_cmd(struct cxl_memdev *cxlmd, static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd, unsigned long arg) { + /* + * Stop servicing ioctls once the device has been unregistered + * which indicates it has been disconnected from its cxlm driver + * context + */ + if (!device_is_registered(&cxlmd->dev)) + return -ENXIO; + switch (cmd) { case CXL_MEM_QUERY_COMMANDS: return cxl_query_cmd(cxlmd, (void __user *)arg); @@ -776,26 +781,42 @@ 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, idx; - inode = file_inode(file); - cxlmd = container_of(inode->i_cdev, typeof(*cxlmd), cdev); + idx = srcu_read_lock(&cxl_memdev_srcu); + rc = __cxl_memdev_ioctl(cxlmd, cmd, arg); + srcu_read_unlock(&cxl_memdev_srcu, idx); - 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 +1070,6 @@ 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); } @@ -1155,21 +1175,12 @@ static void cxlmdev_unregister(void *_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); + synchronize_srcu(&cxl_memdev_srcu); cxlmd->cxlm = NULL; put_device(dev); } -static void cxlmdev_ops_active_release(struct percpu_ref *ref) -{ - struct cxl_memdev *cxlmd = - container_of(ref, typeof(*cxlmd), ops_active); - - complete(&cxlmd->ops_dead); -} - static int cxl_mem_add_memdev(struct cxl_mem *cxlm) { struct pci_dev *pdev = cxlm->pdev; @@ -1181,17 +1192,12 @@ 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. + * @cxlm is released when the driver unbinds so srcu and + * device_is_registered() protect usage of this through @cxlmd. */ 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) @@ -1216,16 +1222,13 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm) return devm_add_action_or_reset(dev->parent, cxlmdev_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, flush 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: + synchronize_srcu(&cxl_memdev_srcu); + ida_free(&cxl_memdev_ida, cxlmd->id); +err_id: kfree(cxlmd); return rc;