From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 F101A304BA4; Tue, 2 Sep 2025 13:18:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756819132; cv=none; b=k5jj/6rjA6ZbX4s7nx52anQYparz3zGWteNYdUsAmw1XJKe6xQ2xxCV5NdWnEaXOh/dLCGCwBeWJKHs+vs7HQL9pq27DvOxAJ6gh5nuTYi6RS7H4RKbEOpi0JSmH1HfnOasqwPPlyI1kWrSedno9SoId4CCYy+VfAfb+dS2gftg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756819132; c=relaxed/simple; bh=3OlIsexLNj280IDiHBciTLojhFBSfNBq82YiRU5Yb4I=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=IjKJs8dLQBGXGSmuwtPA11ucE6XMQJYfTIjovk32RPiwJK++qN5UddiQ6cU0KZZJ0bpnpW8IlwEFQXQGA7/E62LWXDJFIa9guAmho1yH4dbNfsyc0RSleyCBtwClRw7X8ZfwscZz9yvq389Nm3CoMFe9gHz9FFmIAmobKO+OZUM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VjrEBk7/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VjrEBk7/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9DB5AC4CEED; Tue, 2 Sep 2025 13:18:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756819131; bh=3OlIsexLNj280IDiHBciTLojhFBSfNBq82YiRU5Yb4I=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VjrEBk7/GBQB1RNdCrvoc4NxQmwXITuCLuJVjArCdPbII01bVOGn4lGDMU5dZD+7M F6dT7jysa4nSPGT4Vadn6SkSl6IrTqgOJZJHxCkgW2vQjFJUhEAT//mo7nmVC4ZH6e 5rJJ6OF9DEEuKm7lBf8z2GyG6bffNueSHosHWTkNos8/iS7wAP8tIyeTiuT03PHPOk C9xveW26wVKMRDOsqpJgiaK5FKbGtLKpwa3iLa8w7XcpCGKRyDFzkK7EQmXEOxwi3M KORrLTFoj6inwMGJ0vwLgkEX74EGGpSIvag6aB++qMVaYrJsM8CF8QrKmLigt5dAj8 7YEHUy0+ENPIw== Date: Tue, 2 Sep 2025 21:18:47 +0800 From: Tzung-Bi Shih To: Dmitry Torokhov Cc: Benson Leung , linux-input@vger.kernel.org, chrome-platform@lists.linux.dev Subject: Re: [PATCH 0/5] platform/chrome: Fix a race when probing drivers Message-ID: References: <20250828083601.856083-1-tzungbi@kernel.org> Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Aug 29, 2025 at 08:50:01PM +0800, Tzung-Bi Shih wrote: > On Fri, Aug 29, 2025 at 11:28:55AM +0000, Dmitry Torokhov wrote: > > On Thu, Aug 28, 2025 at 08:35:56AM +0000, Tzung-Bi Shih wrote: > > > A race is observed when cros_ec_lpc and cros-ec-keyb are all built as > > > modules. cros_ec_lpc is cros-ec-keyb's parent. However, they can be > > > probed at the same time. > > > > > > Example: > > > > > > + -----------------------------------------------------------------+ > > > | Some init process (e.g. udevd) | deferred_probe_work_func worker | > > > + -----------------------------------------------------------------+ > > > | Probe cros-ec-keyb. | | > > > | - Decide to defer[1]. | | > > > | | A device bound to a driver[2]. | > > > | Probe cros_ec_lpc. | | > > > | - Init the struct[3]. | | > > > | | Retry cros-ec-keyb from the | > > > | | deferred list[4]. | > > > | | - Won't defer again as [3]. | > > > | | - Access uninitialized data in | > > > | | the struct. | > > > | - Register the device. | | > > > + -----------------------------------------------------------------+ > > > > > > [1] https://elixir.bootlin.com/linux/v6.16/source/drivers/input/keyboard/cros_ec_keyb.c#L707 > > > [2] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L405 > > > [3] https://elixir.bootlin.com/linux/v6.16/source/drivers/platform/chrome/cros_ec_lpc.c#L644 > > > [4] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L418 > > > > > > Note that the device link[5] can't help as in the observed environment, > > > the devices are already added via device_add()[6]. > > > > > > [5] https://www.kernel.org/doc/html/latest/driver-api/device_link.html#usage > > > [6] https://elixir.bootlin.com/linux/v6.16/source/drivers/acpi/acpi_platform.c#L177 > > > > > > The series fixes the issue by ensuring the struct is ready for accessing > > > before continuing to probe cros-ec-keyb. > > > > Why is the keyboard platform device instantiated before the transport > > (cros_ec_lpc) is done initializing? I think this is the root of the > > issue... > > I may misunderstand but it seems to me: > > - The ACPI bus enumerated and instantiated the platform devices[6] first. > > - The keyboard platform device was probed when `cros_ec_keyb_driver` > registered. It deferred as its parent's drvdata was NULL[1]. > > - The transport platform device was probed when `cros_ec_lpc_driver` > registered. It set the drvdata[3]. > > - The keyboard platform device was probed again from retrying the deferred > list, by another thread `deferred_probe_work_func`. The parent's drvdata > wasn't NULL and cros_ec_register() for the transport device weren't > finished. The race happened. Hi Dmitry, Does it make sense to you?