From patchwork Tue Mar 12 10:34:22 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sakari Ailus X-Patchwork-Id: 13589820 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC3A57A127 for ; Tue, 12 Mar 2024 10:34:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710239686; cv=none; b=UVbSfyKsSTUM5oXCZLrWJWP2xS9SHvuPAZCm+C6Z6KeowS9vH9BbmSlAYRnV9Wf2uugVqtPTFluog0NIOaUkMr/MJ4otvBZDKC5UZ3LPTnmfkUvFosuAZGZE08t3hXBJMdm15TvIgtrvZXXPJfmCc56sNEczbgnjjiksm+0l4+4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1710239686; c=relaxed/simple; bh=1xlSTuEdeFyONt5K7qt6F4QtCG63Eauf7PTfPM9vWqk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Y9N+89iF8fUdCHYCTRBJxzWbG/5K4v23BvH9UC+d9Q07qwPwoX1BA4SOal5dZA7I4c61QpV1a7oTXQH9tz+Qp5HFsfg34BkNI4/SRkHfhTKZjTHMGbdA8G/PvzoRmk1Rmlq4h1U6KCNFG5jzms5XPJPZc6N4HVXcn2ATXFNYbRg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=none smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=lILlt1sN; arc=none smtp.client-ip=192.198.163.17 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="lILlt1sN" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1710239685; x=1741775685; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=1xlSTuEdeFyONt5K7qt6F4QtCG63Eauf7PTfPM9vWqk=; b=lILlt1sNxDA606q6ZjB/Vtvm8xu3bRDRMy4twNI/gcwckhMoO+ByRPyW vK4DMdNXFdugKitTs6lO+CRewL0KuJ2Ls4xg6OPsTOPwHYXSH4K/f9qb0 +422m+TVZfs5015LK39LXmHHnb0R1URw3ikwRiW+ZN7hFI+M1xwxLsIXr 3nD3UdHWBdIVcTzDOfi9ePUD1fT3vg36Hdl5ATp4o/C8atJRtlBgGjHHD MI2ldDqxinv0gPH/33mCX6e6Io7QyUhNFtrsoUjd7RQSJOa7vooi2/3f/ k6ASCNCKF7nS+h1fOA3JLOFWTF8Z4IRc99Wu2d7l/I5jqqiv4V3/jJv10 A==; X-IronPort-AV: E=McAfee;i="6600,9927,11010"; a="4794349" X-IronPort-AV: E=Sophos;i="6.07,119,1708416000"; d="scan'208";a="4794349" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Mar 2024 03:34:44 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,119,1708416000"; d="scan'208";a="16194124" Received: from turnipsi.fi.intel.com (HELO kekkonen.fi.intel.com) ([10.237.72.44]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Mar 2024 03:34:43 -0700 Received: from svinhufvud.ger.corp.intel.com (localhost [IPv6:::1]) by kekkonen.fi.intel.com (Postfix) with ESMTP id 6884A11F81D; Tue, 12 Mar 2024 12:34:40 +0200 (EET) From: Sakari Ailus To: linux-media@vger.kernel.org Cc: laurent.pinchart@ideasonboard.com, hverkuil@xs4all.nl Subject: [PATCH v3 26/26] media: Documentation: Document media device memory safety helper Date: Tue, 12 Mar 2024 12:34:22 +0200 Message-Id: <20240312103422.216484-27-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20240312103422.216484-1-sakari.ailus@linux.intel.com> References: <20240312103422.216484-1-sakari.ailus@linux.intel.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Document how the best effort memory safety helper for accessing media device works, and that drivers should be converted to refcount the media device. Signed-off-by: Sakari Ailus --- drivers/media/mc/mc-devnode.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/drivers/media/mc/mc-devnode.c b/drivers/media/mc/mc-devnode.c index 8742bd7a3521..e5ae187246d6 100644 --- a/drivers/media/mc/mc-devnode.c +++ b/drivers/media/mc/mc-devnode.c @@ -243,6 +243,32 @@ void media_devnode_init(struct media_devnode *devnode) devnode->minor = -1; } +/* + * Best effort media device lifetime management for old drivers + * + * Drivers that do not manage the lifetime of the media device are provided with + * a best effort lifetime management support. This means that as the driver does + * not release the media device once all users are gone but when the device is + * unbound, there are bound to be (brief) moments when released memory may get + * accessed. All drivers should be converted to release their memory at a safe + * time, i.e. provide a release callback in struct media_file_operations to do + * so. This is especially important for drivers for devices that are + * unpluggable, e.g. USB devices. + * + * A second struct device is used to manage the lifetime of a helper object, + * struct media_devnode_compat_ref. For a media device, one is initialised in + * media_devnode_register and put in media_devnode_unregister. This object is + * also used as the device of the media character device so file handles to the + * media device have a reference to this object. When the media device is + * released, any file handle retains a reference to this helper that also + * contains the media device's registration status. If a media device is + * released and a user space process attempts to access the file handle, an + * error is returned. + * + * The struct device in struct media_devnode is put at media_device_cleanup and + * uses an empty release callback, reflecting the expectation the driver will + * release the memory of the media device at unbind time. + */ int __must_check media_devnode_register(struct media_devnode *devnode, struct module *owner) {