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 46A36C6FD1D for ; Tue, 14 Mar 2023 14:20:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230031AbjCNOUW (ORCPT ); Tue, 14 Mar 2023 10:20:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230152AbjCNOTn (ORCPT ); Tue, 14 Mar 2023 10:19:43 -0400 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 76F5016337; Tue, 14 Mar 2023 07:19:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1678803566; x=1710339566; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=1SxLjl6qhTMi8K6jcf0bH0P37z8ztwqynXPKYwnqmlg=; b=IN0rU4kHKRotaLYli9ew55SpzUI5sdkNvl5HbOs2cAPX4Da5owIWN8Z1 zBWUN6CoNz0SkF899cIKKR7SCjIqjXyECKUObwZHSZpe5M258Za8WFUZR XWCBUbK9OqdxFzbb5ASQ6JqB6hvq6DxECytu1qeGh84eSoZqL9cprh9up dSYulOKUEG8FnUU21XSia8syz4MntzDCH+z23Qz9VVwAUoMP/zy0Rp1Kl fyqbkkngw2giJ6Sx0h+8Ex4uZ/YVcYWxarmJns7CJUjgREuoTQhdCB/D2 3ZsAWx1XdeDGccGA3QKHu4rkP515v2HadlCSQIAQOaQS/SRdmQprZSNAY g==; X-IronPort-AV: E=McAfee;i="6500,9779,10649"; a="321284682" X-IronPort-AV: E=Sophos;i="5.98,260,1673942400"; d="scan'208";a="321284682" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Mar 2023 07:19:25 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10649"; a="656363215" X-IronPort-AV: E=Sophos;i="5.98,260,1673942400"; d="scan'208";a="656363215" Received: from mjtillin-mobl.ger.corp.intel.com (HELO localhost.localdomain) ([10.213.236.227]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Mar 2023 07:19:21 -0700 From: Tvrtko Ursulin To: Intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Tejun Heo , Johannes Weiner , Zefan Li , Dave Airlie , Daniel Vetter , Rob Clark , =?UTF-8?q?St=C3=A9phane=20Marchesin?= , "T . J . Mercier" , Kenny.Ho@amd.com, =?UTF-8?q?Christian=20K=C3=B6nig?= , Brian Welty , Tvrtko Ursulin , Daniel Vetter Subject: [RFC 02/10] drm: Update file owner during use Date: Tue, 14 Mar 2023 14:18:56 +0000 Message-Id: <20230314141904.1210824-3-tvrtko.ursulin@linux.intel.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20230314141904.1210824-1-tvrtko.ursulin@linux.intel.com> References: <20230314141904.1210824-1-tvrtko.ursulin@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Tvrtko Ursulin With the typical model where the display server opends the file descriptor and then hands it over to the client we were showing stale data in debugfs. Fix it by updating the drm_file->pid on ioctl access from a different process. The field is also made RCU protected to allow for lockless readers. Update side is protected with dev->filelist_mutex. Before: $ cat /sys/kernel/debug/dri/0/clients command pid dev master a uid magic Xorg 2344 0 y y 0 0 Xorg 2344 0 n y 0 2 Xorg 2344 0 n y 0 3 Xorg 2344 0 n y 0 4 After: $ cat /sys/kernel/debug/dri/0/clients command tgid dev master a uid magic Xorg 830 0 y y 0 0 xfce4-session 880 0 n y 0 1 xfwm4 943 0 n y 0 2 neverball 1095 0 n y 0 3 Signed-off-by: Tvrtko Ursulin Cc: "Christian König" Cc: Daniel Vetter --- drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 6 ++-- drivers/gpu/drm/drm_auth.c | 3 +- drivers/gpu/drm/drm_debugfs.c | 10 ++++--- drivers/gpu/drm/drm_file.c | 40 +++++++++++++++++++++++-- drivers/gpu/drm/drm_ioctl.c | 3 ++ drivers/gpu/drm/nouveau/nouveau_drm.c | 5 +++- drivers/gpu/drm/vmwgfx/vmwgfx_gem.c | 6 ++-- include/drm/drm_file.h | 13 ++++++-- 8 files changed, 71 insertions(+), 15 deletions(-) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c index 863cb668e000..67ce634992f6 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c @@ -960,6 +960,7 @@ static int amdgpu_debugfs_gem_info_show(struct seq_file *m, void *unused) list_for_each_entry(file, &dev->filelist, lhead) { struct task_struct *task; struct drm_gem_object *gobj; + struct pid *pid; int id; /* @@ -969,8 +970,9 @@ static int amdgpu_debugfs_gem_info_show(struct seq_file *m, void *unused) * Therefore, we need to protect this ->comm access using RCU. */ rcu_read_lock(); - task = pid_task(file->pid, PIDTYPE_TGID); - seq_printf(m, "pid %8d command %s:\n", pid_nr(file->pid), + pid = rcu_dereference(file->pid); + task = pid_task(pid, PIDTYPE_TGID); + seq_printf(m, "pid %8d command %s:\n", pid_nr(pid), task ? task->comm : ""); rcu_read_unlock(); diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index cf92a9ae8034..2ed2585ded37 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -235,7 +235,8 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) static int drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv) { - if (file_priv->pid == task_pid(current) && file_priv->was_master) + if (file_priv->was_master && + rcu_access_pointer(file_priv->pid) == task_pid(current)) return 0; if (!capable(CAP_SYS_ADMIN)) diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c index 4855230ba2c6..b46f5ceb24c6 100644 --- a/drivers/gpu/drm/drm_debugfs.c +++ b/drivers/gpu/drm/drm_debugfs.c @@ -90,15 +90,17 @@ static int drm_clients_info(struct seq_file *m, void *data) */ mutex_lock(&dev->filelist_mutex); list_for_each_entry_reverse(priv, &dev->filelist, lhead) { - struct task_struct *task; bool is_current_master = drm_is_current_master(priv); + struct task_struct *task; + struct pid *pid; - rcu_read_lock(); /* locks pid_task()->comm */ - task = pid_task(priv->pid, PIDTYPE_TGID); + rcu_read_lock(); /* Locks priv->pid and pid_task()->comm! */ + pid = rcu_dereference(priv->pid); + task = pid_task(pid, PIDTYPE_TGID); uid = task ? __task_cred(task)->euid : GLOBAL_ROOT_UID; seq_printf(m, "%20s %5d %3d %c %c %5d %10u\n", task ? task->comm : "", - pid_vnr(priv->pid), + pid_vnr(pid), priv->minor->index, is_current_master ? 'y' : 'n', priv->authenticated ? 'y' : 'n', diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c index c1018c470047..f2f8175ece15 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -156,7 +156,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) if (!file) return ERR_PTR(-ENOMEM); - file->pid = get_pid(task_tgid(current)); + rcu_assign_pointer(file->pid, get_pid(task_tgid(current))); file->minor = minor; /* for compatibility root is always authenticated */ @@ -196,7 +196,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) drm_syncobj_release(file); if (drm_core_check_feature(dev, DRIVER_GEM)) drm_gem_release(dev, file); - put_pid(file->pid); + put_pid(rcu_access_pointer(file->pid)); kfree(file); return ERR_PTR(ret); @@ -287,7 +287,7 @@ void drm_file_free(struct drm_file *file) WARN_ON(!list_empty(&file->event_list)); - put_pid(file->pid); + put_pid(rcu_access_pointer(file->pid)); kfree(file); } @@ -501,6 +501,40 @@ int drm_release(struct inode *inode, struct file *filp) } EXPORT_SYMBOL(drm_release); +void drm_file_update_pid(struct drm_file *filp) +{ + struct drm_device *dev; + struct pid *pid, *old; + + /* + * Master nodes need to keep the original ownership in order for + * drm_master_check_perm to keep working correctly. (See comment in + * drm_auth.c.) + */ + if (filp->was_master) + return; + + pid = task_tgid(current); + + /* + * Quick unlocked check since the model is a single handover followed by + * exclusive repeated use. + */ + if (pid == rcu_access_pointer(filp->pid)) + return; + + dev = filp->minor->dev; + mutex_lock(&dev->filelist_mutex); + old = rcu_replace_pointer(filp->pid, pid, 1); + mutex_unlock(&dev->filelist_mutex); + + if (pid != old) { + get_pid(pid); + synchronize_rcu(); + put_pid(old); + } +} + /** * drm_release_noglobal - release method for DRM file * @inode: device inode diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index 7c9d66ee917d..305b18d9d7b6 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -775,6 +775,9 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata, struct drm_device *dev = file_priv->minor->dev; int retcode; + /* Update drm_file owner if fd was passed along. */ + drm_file_update_pid(file_priv); + if (drm_dev_is_unplugged(dev)) return -ENODEV; diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c index cc7c5b4a05fd..57aeaf7af613 100644 --- a/drivers/gpu/drm/nouveau/nouveau_drm.c +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c @@ -1095,7 +1095,10 @@ nouveau_drm_open(struct drm_device *dev, struct drm_file *fpriv) } get_task_comm(tmpname, current); - snprintf(name, sizeof(name), "%s[%d]", tmpname, pid_nr(fpriv->pid)); + rcu_read_lock(); + snprintf(name, sizeof(name), "%s[%d]", + tmpname, pid_nr(rcu_dereference(fpriv->pid))); + rcu_read_unlock(); if (!(cli = kzalloc(sizeof(*cli), GFP_KERNEL))) { ret = -ENOMEM; diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c index c0da89e16e6f..a07e5b7e2f2f 100644 --- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c @@ -232,6 +232,7 @@ static int vmw_debugfs_gem_info_show(struct seq_file *m, void *unused) list_for_each_entry(file, &dev->filelist, lhead) { struct task_struct *task; struct drm_gem_object *gobj; + struct pid *pid; int id; /* @@ -241,8 +242,9 @@ static int vmw_debugfs_gem_info_show(struct seq_file *m, void *unused) * Therefore, we need to protect this ->comm access using RCU. */ rcu_read_lock(); - task = pid_task(file->pid, PIDTYPE_TGID); - seq_printf(m, "pid %8d command %s:\n", pid_nr(file->pid), + pid = rcu_dereference(file->pid); + task = pid_task(pid, PIDTYPE_TGID); + seq_printf(m, "pid %8d command %s:\n", pid_nr(pid), task ? task->comm : ""); rcu_read_unlock(); diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h index 0d1f853092ab..27d545131d4a 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -255,8 +255,15 @@ struct drm_file { /** @master_lookup_lock: Serializes @master. */ spinlock_t master_lookup_lock; - /** @pid: Process that opened this file. */ - struct pid *pid; + /** + * @pid: Process that is using this file. + * + * Must only be dereferenced under a rcu_read_lock or equivalent. + * + * Updates are guarded with dev->filelist_mutex and reference must be + * dropped after a RCU grace period to accommodate lockless readers. + */ + struct pid __rcu *pid; /** @magic: Authentication magic, see @authenticated. */ drm_magic_t magic; @@ -415,6 +422,8 @@ static inline bool drm_is_accel_client(const struct drm_file *file_priv) return file_priv->minor->type == DRM_MINOR_ACCEL; } +void drm_file_update_pid(struct drm_file *); + int drm_open(struct inode *inode, struct file *filp); int drm_open_helper(struct file *filp, struct drm_minor *minor); ssize_t drm_read(struct file *filp, char __user *buffer, -- 2.37.2