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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7C5B6C6FD1D for ; Tue, 4 Apr 2023 13:34:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235181AbjDDNe3 (ORCPT ); Tue, 4 Apr 2023 09:34:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235225AbjDDNeR (ORCPT ); Tue, 4 Apr 2023 09:34:17 -0400 Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net [IPv6:2001:4b98:dc4:8::224]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FD223C06; Tue, 4 Apr 2023 06:33:55 -0700 (PDT) Received: (Authenticated sender: alexis.lothore@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id 0DD9AE000D; Tue, 4 Apr 2023 13:33:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1680615234; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=dhPKsedyNaIm395Jon3eIezMwB2v8WnHlUJJmpukY9g=; b=Thx8U5pQS6MGp3KVFvjDkn8adG0aYVFH99okR43UMr9h3oYL42FzBRZ/WaocJGpGLIvVUp Chw5l83T9ejeznKsxGtkTIuNqy3jD7FJbzBo32r7wA+vwMzJ0oJ7ePuJYeQswMhkMk7eQD vKujDW7RCVPNpk9k55dqoxwjjYX4J9RgnT29/R3qYm8uRCqkuolEETawgCPVIwAvM6vB1p PQ0LNH2X/fSIVXi7xdemSa5yjo6KXOG15DYii498tf7xDHiOBIin7EzHcqi1W0RI4rU5qL wgQ2Qrz/TSZ4UA92hz07Zw/U4CDvF64Loxu1rF81CBNcoFOsZGt5/fDVi61Viw== From: alexis.lothore@bootlin.com To: mdf@kernel.org, hao.wu@intel.com, yilun.xu@intel.com, trix@redhat.com, russell.h.weight@intel.com, linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org Cc: thomas.petazzoni@bootlin.com, nicolas.carrier@orolia.com Subject: [PATCH 0/1] warning on FPGA bridge registration Date: Tue, 4 Apr 2023 15:31:01 +0200 Message-Id: <20230404133102.2837535-1-alexis.lothore@bootlin.com> X-Mailer: git-send-email 2.40.0 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: Alexis Lothoré Hello, While upgrading a kernel 5.10.x to kernel 6.1.x, I observe some warnings. The target platform is a socfpga (Cyclone V). The warning has the following trace: [ 26.725222] WARNING: CPU: 0 PID: 1 at lib/refcount.c:25 kobject_get (./include/linux/refcount.h:199 ./include/linux/refcount.h:250 ./include/linux/refcount.h:267 ./include/linux/kref.h:45 lib/kobject.c:635) [ 26.732380] refcount_t: addition on 0; use-after-free. [ 26.737501] Modules linked in: [ 26.747935] Hardware name: Altera SOCFPGA [ 26.751939] unwind_backtrace from show_stack (arch/arm/kernel/traps.c:255) [ 26.757175] show_stack from dump_stack_lvl (lib/dump_stack.c:107 (discriminator 1)) [ 26.762230] dump_stack_lvl from __warn (kernel/panic.c:632 kernel/panic.c:679) [ 26.767032] __warn from warn_slowpath_fmt (./include/asm-generic/preempt.h:69 ./include/linux/context_tracking.h:154 kernel/panic.c:705) [ 26.772177] warn_slowpath_fmt from kobject_get (./include/linux/refcount.h:199 ./include/linux/refcount.h:250 ./include/linux/refcount.h:267 ./include/linux/kref.h:45 lib/kobject.c:635) [ 26.777580] kobject_get from device_add (drivers/base/core.c:3760 drivers/base/core.c:3584) [ 26.782464] device_add from of_platform_device_create_pdata (drivers/of/platform.c:190) [ 26.788994] of_platform_device_create_pdata from of_platform_bus_create (drivers/of/platform.c:390) [ 26.796732] of_platform_bus_create from of_platform_populate (drivers/of/platform.c:482) [ 26.803432] of_platform_populate from fpga_bridge_register (drivers/fpga/fpga-bridge.c:365) [ 26.809967] fpga_bridge_register from alt_fpga_bridge_probe (drivers/fpga/altera-hps2fpga.c:185) [ 26.816674] alt_fpga_bridge_probe from platform_probe (drivers/base/platform.c:1401) [ 26.822682] platform_probe from really_probe (drivers/base/dd.c:560 drivers/base/dd.c:639) [ 26.827995] really_probe from __driver_probe_device (drivers/base/dd.c:778) [ 26.833919] __driver_probe_device from driver_probe_device (drivers/base/dd.c:809) [ 26.840363] driver_probe_device from __driver_attach (drivers/base/dd.c:1195) [ 26.846460] __driver_attach from bus_for_each_dev (drivers/base/bus.c:300) [ 26.852122] bus_for_each_dev from bus_add_driver (drivers/base/bus.c:619) [ 26.857870] bus_add_driver from driver_register (drivers/base/driver.c:247) [ 26.863449] driver_register from do_one_initcall (./include/linux/jump_label.h:259 ./include/linux/jump_label.h:269 ./include/trace/events/initcall.h:48 init/main.c:1304) [ 26.869116] do_one_initcall from kernel_init_freeable (init/main.c:1375 init/main.c:1392 init/main.c:1411 init/main.c:1631) [ 26.875296] kernel_init_freeable from kernel_init (init/main.c:1521) [ 26.881047] kernel_init from ret_from_fork (arch/arm/kernel/entry-common.S:149) [ 26.886097] Exception stack(0xf0831fb0 to 0xf0831ff8) [ 26.891138] 1fa0: 00000000 00000000 00000000 00000000 [ 26.899292] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 [ 26.907442] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 >From my understanding, the warning occurs because the device passed to of_platform_populate() in fpga_bridge_register() is not initialized. As a consequence, when it will eventually try to get a reference on parent device to create new child, it will find an uninitialized kobject and raise the warning. My guess is that the issue occurs since commit 0d70af3c2530 (and a revert tends to prove it). Before this rework, device initialization and addition were done before of_platform_populate. This commit has merged fpga_bridge_create() and fpga_bridge_register() (and while doing so, it has merged device_initialize() and device_add() into device_register()), but in the meantime it has moved device_register() AFTER of_platform_populate() A naive attempt to revert to previous behavior (device init/add before of_platform_populate) can be found with the following patch, but since my understanding of fpga framework is still quite limited, please let me know if I am missing something. Alexis Lothoré (1): fpga: bridge: properly initialize bridge device before populating children drivers/fpga/fpga-bridge.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) -- 2.40.0