Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751242AbaBKGv1 (ORCPT ); Tue, 11 Feb 2014 01:51:27 -0500 Received: from mx0a-0016f401.pphosted.com ([67.231.148.174]:58761 "EHLO mx0a-0016f401.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbaBKGvZ (ORCPT ); Tue, 11 Feb 2014 01:51:25 -0500 From: To: , , , , , CC: , Jane Li , Daniel Vetter Subject: [PATCH] printk: fix one circular lockdep warning about console_lock Date: Tue, 11 Feb 2014 14:50:00 +0800 Message-ID: <1392101400-14550-1-git-send-email-jiel@marvell.com> X-Mailer: git-send-email 1.7.9.5 MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.11.87,1.0.14,0.0.0000 definitions=2014-02-11_03:2014-02-10,2014-02-11,1970-01-01 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=7.0.1-1305240000 definitions=main-1402100241 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jane Li This patch tries to fix a warning about possible circular locking dependency. If do in following sequence: enter suspend -> resume -> plug-out CPUx (echo 0 > cpux/online) lockdep will show warning as following: ====================================================== [ INFO: possible circular locking dependency detected ] 3.10.0 #2 Tainted: G O ------------------------------------------------------- sh/1271 is trying to acquire lock: (console_lock){+.+.+.}, at: [] console_cpu_notify+0x20/0x2c but task is already holding lock: (cpu_hotplug.lock){+.+.+.}, at: [] cpu_hotplug_begin+0x2c/0x58 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (cpu_hotplug.lock){+.+.+.}: [] lock_acquire+0x98/0x12c [] mutex_lock_nested+0x50/0x3d8 [] cpu_hotplug_begin+0x2c/0x58 [] _cpu_up+0x24/0x154 [] cpu_up+0x64/0x84 [] smp_init+0x9c/0xd4 [] kernel_init_freeable+0x78/0x1c8 [] kernel_init+0x8/0xe4 [] ret_from_fork+0x14/0x2c -> #1 (cpu_add_remove_lock){+.+.+.}: [] lock_acquire+0x98/0x12c [] mutex_lock_nested+0x50/0x3d8 [] disable_nonboot_cpus+0x8/0xe8 [] suspend_devices_and_enter+0x214/0x448 [] pm_suspend+0x1e4/0x284 [] try_to_suspend+0xa4/0xbc [] process_one_work+0x1c4/0x4fc [] worker_thread+0x138/0x37c [] kthread+0xa4/0xb0 [] ret_from_fork+0x14/0x2c -> #0 (console_lock){+.+.+.}: [] __lock_acquire+0x1b38/0x1b80 [] lock_acquire+0x98/0x12c [] console_lock+0x54/0x68 [] console_cpu_notify+0x20/0x2c [] notifier_call_chain+0x44/0x84 [] __cpu_notify+0x2c/0x48 [] cpu_notify_nofail+0x8/0x14 [] _cpu_down+0xf4/0x258 [] cpu_down+0x24/0x40 [] store_online+0x30/0x74 [] dev_attr_store+0x18/0x24 [] sysfs_write_file+0x16c/0x19c [] vfs_write+0xb4/0x190 [] SyS_write+0x3c/0x70 [] ret_fast_syscall+0x0/0x48 Chain exists of: console_lock --> cpu_add_remove_lock --> cpu_hotplug.lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(cpu_hotplug.lock); lock(cpu_add_remove_lock); lock(cpu_hotplug.lock); lock(console_lock); *** DEADLOCK *** There are three locks involved in two sequence: a) pm suspend: console_lock (@suspend_console()) cpu_add_remove_lock (@disable_nonboot_cpus()) cpu_hotplug.lock (@_cpu_down()) b) Plug-out CPUx: cpu_add_remove_lock (@(cpu_down()) cpu_hotplug.lock (@_cpu_down()) console_lock (@console_cpu_notify()) => Lockdeps prints warning log. There should be not real deadlock, as flag of console_suspended can protect this. Printk registers cpu hotplug notify function. When CPUx is plug-out/in, always execute console_lock() and console_unlock(). This patch modifies that with console_trylock() and console_unlock(). Then use that instead of the unconditional console_lock/unlock pair to avoid the warning. Signed-off-by: Jane Li Signed-off-by: Daniel Vetter --- kernel/printk/printk.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index b1d255f..e7a0525 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1893,6 +1893,20 @@ void resume_console(void) } /** + * console_flush - flush dmesg if console isn't suspended + * + * console_unlock always flushes the dmesg buffer, so just try to + * grab&drop the console lock. If that fails we know that the current + * holder will eventually drop the console lock and so flush the dmesg + * buffers at the earliest possible time. + */ +void console_flush(void) +{ + if (console_trylock()) + console_unlock(); +} + +/** * console_cpu_notify - print deferred console messages after CPU hotplug * @self: notifier struct * @action: CPU hotplug event @@ -1911,8 +1925,7 @@ static int console_cpu_notify(struct notifier_block *self, case CPU_DEAD: case CPU_DOWN_FAILED: case CPU_UP_CANCELED: - console_lock(); - console_unlock(); + console_flush(); } return NOTIFY_OK; } -- 1.7.9.5 -- 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/