Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756829Ab2BMOxb (ORCPT ); Mon, 13 Feb 2012 09:53:31 -0500 Received: from mail-pz0-f46.google.com ([209.85.210.46]:54556 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756740Ab2BMOxU convert rfc822-to-8bit (ORCPT ); Mon, 13 Feb 2012 09:53:20 -0500 MIME-Version: 1.0 In-Reply-To: <20120208124147.GF16334@legolas.emea.dhcp.ti.com> References: <20120208124147.GF16334@legolas.emea.dhcp.ti.com> Date: Mon, 13 Feb 2012 22:53:20 +0800 Message-ID: Subject: Re: Possible circular locking dependency (3.3-rc2) From: Ming Lei To: balbi@ti.com Cc: Grant Likely , Linus Walleij , Linux OMAP Mailing List , Linux Kernel Mailing List , Linux ARM Kernel Mailing List Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6730 Lines: 148 Hi, On Wed, Feb 8, 2012 at 8:41 PM, Felipe Balbi wrote: > Hi guys, > > I have just triggered the folllowing: > > [ ? 84.860321] ====================================================== > [ ? 84.860321] [ INFO: possible circular locking dependency detected ] > [ ? 84.860321] 3.3.0-rc2-00026-ge4e8a39 #474 Not tainted > [ ? 84.860321] ------------------------------------------------------- > [ ? 84.860321] bash/949 is trying to acquire lock: > [ ? 84.860321] ?(sysfs_lock){+.+.+.}, at: [] gpio_value_store+0x24/0xcc > [ ? 84.860321] > [ ? 84.860321] but task is already holding lock: > [ ? 84.860321] ?(s_active#22){++++.+}, at: [] sysfs_write_file+0xdc/0x184 > [ ? 84.911468] > [ ? 84.911468] which lock already depends on the new lock. > [ ? 84.911468] > [ ? 84.920043] > [ ? 84.920043] the existing dependency chain (in reverse order) is: > [ ? 84.920043] > [ ? 84.927886] -> #1 (s_active#22){++++.+}: > [ ? 84.927886] ? ? ? ?[] check_prevs_add+0xdc/0x150 > [ ? 84.927886] ? ? ? ?[] validate_chain.clone.24+0x564/0x694 > [ ? 84.927886] ? ? ? ?[] __lock_acquire+0x49c/0x980 > [ ? 84.951660] ? ? ? ?[] lock_acquire+0x98/0x100 > [ ? 84.951660] ? ? ? ?[] sysfs_deactivate+0xb0/0x100 > [ ? 84.962982] ? ? ? ?[] sysfs_addrm_finish+0x2c/0x6c > [ ? 84.962982] ? ? ? ?[] sysfs_remove_dir+0x84/0x98 > [ ? 84.962982] ? ? ? ?[] kobject_del+0x10/0x78 > [ ? 84.974670] ? ? ? ?[] device_del+0x140/0x170 > [ ? 84.974670] ? ? ? ?[] device_unregister+0xc/0x18 > [ ? 84.985382] ? ? ? ?[] gpio_unexport+0xbc/0xdc > [ ? 84.985382] ? ? ? ?[] gpio_free+0x14/0xfc > [ ? 85.001708] ? ? ? ?[] unexport_store+0x78/0x8c > [ ? 85.001708] ? ? ? ?[] class_attr_store+0x18/0x24 > [ ? 85.007293] ? ? ? ?[] sysfs_write_file+0x100/0x184 > [ ? 85.018981] ? ? ? ?[] vfs_write+0xb4/0x148 > [ ? 85.018981] ? ? ? ?[] sys_write+0x40/0x70 > [ ? 85.018981] ? ? ? ?[] ret_fast_syscall+0x0/0x3c > [ ? 85.035003] > [ ? 85.035003] -> #0 (sysfs_lock){+.+.+.}: > [ ? 85.035003] ? ? ? ?[] check_prev_add+0x680/0x698 > [ ? 85.035003] ? ? ? ?[] check_prevs_add+0xdc/0x150 > [ ? 85.052093] ? ? ? ?[] validate_chain.clone.24+0x564/0x694 > [ ? 85.052093] ? ? ? ?[] __lock_acquire+0x49c/0x980 > [ ? 85.052093] ? ? ? ?[] lock_acquire+0x98/0x100 > [ ? 85.069885] ? ? ? ?[] mutex_lock_nested+0x3c/0x2f4 > [ ? 85.069885] ? ? ? ?[] gpio_value_store+0x24/0xcc > [ ? 85.069885] ? ? ? ?[] dev_attr_store+0x18/0x24 > [ ? 85.087158] ? ? ? ?[] sysfs_write_file+0x100/0x184 > [ ? 85.087158] ? ? ? ?[] vfs_write+0xb4/0x148 > [ ? 85.098297] ? ? ? ?[] sys_write+0x40/0x70 > [ ? 85.098297] ? ? ? ?[] ret_fast_syscall+0x0/0x3c > [ ? 85.109069] > [ ? 85.109069] other info that might help us debug this: > [ ? 85.109069] > [ ? 85.117462] ?Possible unsafe locking scenario: > [ ? 85.117462] > [ ? 85.117462] ? ? ? ?CPU0 ? ? ? ? ? ? ? ? ? ?CPU1 > [ ? 85.128417] ? ? ? ?---- ? ? ? ? ? ? ? ? ? ?---- > [ ? 85.128417] ? lock(s_active#22); > [ ? 85.128417] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?lock(sysfs_lock); > [ ? 85.128417] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?lock(s_active#22); > [ ? 85.142486] ? lock(sysfs_lock); > [ ? 85.151794] > [ ? 85.151794] ?*** DEADLOCK *** > [ ? 85.151794] > [ ? 85.151794] 2 locks held by bash/949: > [ ? 85.158020] ?#0: ?(&buffer->mutex){+.+.+.}, at: [] sysfs_write_file+0x28/0x184 > [ ? 85.170349] ?#1: ?(s_active#22){++++.+}, at: [] sysfs_write_file+0xdc/0x184 > [ ? 85.170349] > [ ? 85.178588] stack backtrace: > [ ? 85.178588] [] (unwind_backtrace+0x0/0xf0) from [] (print_circular_bug+0x100/0x114) > [ ? 85.193023] [] (print_circular_bug+0x100/0x114) from [] (check_prev_add+0x680/0x698) > [ ? 85.193023] [] (check_prev_add+0x680/0x698) from [] (check_prevs_add+0xdc/0x150) > [ ? 85.212524] [] (check_prevs_add+0xdc/0x150) from [] (validate_chain.clone.24+0x564/0x694) > [ ? 85.212524] [] (validate_chain.clone.24+0x564/0x694) from [] (__lock_acquire+0x49c/0x980) > [ ? 85.233306] [] (__lock_acquire+0x49c/0x980) from [] (lock_acquire+0x98/0x100) > [ ? 85.233306] [] (lock_acquire+0x98/0x100) from [] (mutex_lock_nested+0x3c/0x2f4) > [ ? 85.242614] [] (mutex_lock_nested+0x3c/0x2f4) from [] (gpio_value_store+0x24/0xcc) > [ ? 85.261840] [] (gpio_value_store+0x24/0xcc) from [] (dev_attr_store+0x18/0x24) > [ ? 85.261840] [] (dev_attr_store+0x18/0x24) from [] (sysfs_write_file+0x100/0x184) > [ ? 85.271240] [] (sysfs_write_file+0x100/0x184) from [] (vfs_write+0xb4/0x148) > [ ? 85.290008] [] (vfs_write+0xb4/0x148) from [] (sys_write+0x40/0x70) > [ ? 85.298400] [] (sys_write+0x40/0x70) from [] (ret_fast_syscall+0x0/0x3c) > -bash: echo: write error: Operation not permitted > > the way to trigger is: > > > root@legolas:~# cd /sys/class/gpio/ > root@legolas:/sys/class/gpio# echo 2 > export > root@legolas:/sys/class/gpio# echo 2 > unexport > root@legolas:/sys/class/gpio# echo 2 > export > root@legolas:/sys/class/gpio# cd gpio2/ > root@legolas:/sys/class/gpio/gpio2# echo 1 > value Looks 'sysfs_lock' needn't to be held for unregister, so the patch below may fix the problem. diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index 17fdf4b..d773540 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -873,6 +873,7 @@ void gpio_unexport(unsigned gpio) { struct gpio_desc *desc; int status = 0; + struct device *dev = NULL; if (!gpio_is_valid(gpio)) { status = -EINVAL; @@ -884,19 +885,20 @@ void gpio_unexport(unsigned gpio) desc = &gpio_desc[gpio]; if (test_bit(FLAG_EXPORT, &desc->flags)) { - struct device *dev = NULL; dev = class_find_device(&gpio_class, NULL, desc, match_export); if (dev) { gpio_setup_irq(desc, dev, 0); clear_bit(FLAG_EXPORT, &desc->flags); - put_device(dev); - device_unregister(dev); } else status = -ENODEV; } mutex_unlock(&sysfs_lock); + if (dev) { + device_unregister(dev); + put_device(dev); + } done: if (status) pr_debug("%s: gpio%d status %d\n", __func__, gpio, status); thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/