From patchwork Wed Jul 12 11:45:54 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Tvrtko Ursulin X-Patchwork-Id: 13310208 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5794CEB64DA for ; Wed, 12 Jul 2023 11:48:10 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 845AA10E4F5; Wed, 12 Jul 2023 11:47:51 +0000 (UTC) Received: from mga12.intel.com (mga12.intel.com [192.55.52.136]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2195510E4EE; Wed, 12 Jul 2023 11:47:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1689162468; x=1720698468; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=eDOXw0tb/xqHsfV2SZXPsdGPgQMYGO3n3Mu/+yfDMf0=; b=YwRFG1lVrEEVpYfDi+M0LEALq8mrhXVoFagRtJhB3LOzbsxRMW08u8sN RflAjNsWmuacOmXRZSzbZY/tvDJitZcn1nsFI3TTsBD0R14Nl7WFG9ErU wg2L6t4a19SWS2wjDGr1sNfQLSj6GgZXOE8qHDVbjs75FhTD+aKCZVzWw reS8dM/1g3A9JLbe4evX1hVCFQSFHkhPvmS3TLX1guzv++yf9W24dDEDN yHTF/BMcQp1rpdHDIFSx2fYRxlMckwhwOz/pSRNyf8gre9MArRMcFqApH yNPitJkcRPvbuXDqcgHuazuI5KW+fQwxCiaAMJuf6XDGQRELKEahFH3+D w==; X-IronPort-AV: E=McAfee;i="6600,9927,10768"; a="344469169" X-IronPort-AV: E=Sophos;i="6.01,199,1684825200"; d="scan'208";a="344469169" Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2023 04:46:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10768"; a="866094106" X-IronPort-AV: E=Sophos;i="6.01,199,1684825200"; d="scan'208";a="866094106" Received: from eamonnob-mobl1.ger.corp.intel.com (HELO localhost.localdomain) ([10.213.237.202]) by fmsmga001-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Jul 2023 04:46:36 -0700 From: Tvrtko Ursulin To: Intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Subject: [PATCH 06/17] drm: Update file owner during use Date: Wed, 12 Jul 2023 12:45:54 +0100 Message-Id: <20230712114605.519432-7-tvrtko.ursulin@linux.intel.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230712114605.519432-1-tvrtko.ursulin@linux.intel.com> References: <20230712114605.519432-1-tvrtko.ursulin@linux.intel.com> MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Rob Clark , Brian Welty , Kenny.Ho@amd.com, Tvrtko Ursulin , Daniel Vetter , Johannes Weiner , Emil Velikov , linux-kernel@vger.kernel.org, =?utf-8?q?St=C3=A9phane_Marchesin?= , =?utf-8?q?Chris?= =?utf-8?q?tian_K=C3=B6nig?= , Zefan Li , Dave Airlie , Tejun Heo , cgroups@vger.kernel.org, "T . J . Mercier" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" From: Tvrtko Ursulin With the typical model where the display server opens 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 *) More detailed and historically accurate description of various handover implementation kindly provided by Emil Velikov: """ The traditional model, the server was the orchestrator managing the primary device node. From the fd, to the master status and authentication. But looking at the fd alone, this has varied across the years. IIRC in the DRI1 days, Xorg (libdrm really) would have a list of open fd(s) and reuse those whenever needed, DRI2 the client was responsible for open() themselves and with DRI3 the fd was passed to the client. Around the inception of DRI3 and systemd-logind, the latter became another possible orchestrator. Whereby Xorg and Wayland compositors could ask it for the fd. For various reasons (hysterical and genuine ones) Xorg has a fallback path going the open(), whereas Wayland compositors are moving to solely relying on logind... some never had fallback even. Over the past few years, more projects have emerged which provide functionality similar (be that on API level, Dbus, or otherwise) to systemd-logind. """ v2: * Fixed typo in commit text and added a fine historical explanation from Emil. Signed-off-by: Tvrtko Ursulin Cc: "Christian König" Cc: Daniel Vetter Acked-by: Christian König Reviewed-by: Emil Velikov --- 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 74055cba3dc9..849097dff02b 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c @@ -963,6 +963,7 @@ 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; /* @@ -972,8 +973,9 @@ 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 883d83bc0e3d..e692770ef6d3 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -160,7 +160,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) /* Get a unique identifier for fdinfo: */ file->client_id = atomic64_inc_return(&ident); - 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 */ @@ -200,7 +200,7 @@ 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); @@ -291,7 +291,7 @@ 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); } @@ -505,6 +505,40 @@ 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 8e9afe7af19c..78f9387e79fe 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -774,6 +774,9 @@ 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 ca3bb8075357..cd15759815a8 100644 --- a/drivers/gpu/drm/nouveau/nouveau_drm.c +++ b/drivers/gpu/drm/nouveau/nouveau_drm.c @@ -1101,7 +1101,10 @@ 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 966912053cb0..c76249d5467e 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -256,8 +256,15 @@ 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; /** @client_id: A unique id for fdinfo */ u64 client_id; @@ -420,6 +427,8 @@ 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,