From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753287AbaKDMkW (ORCPT ); Tue, 4 Nov 2014 07:40:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43670 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562AbaKDMkU (ORCPT ); Tue, 4 Nov 2014 07:40:20 -0500 From: Vitaly Kuznetsov To: "K. Y. Srinivasan" , Haiyang Zhang Cc: Greg Kroah-Hartman , devel@linuxdriverproject.org, linux-kernel@vger.kernel.org Subject: [PATCH] Drivers: hv: vmbus: Fix a race condition when unregistering a device Date: Tue, 4 Nov 2014 13:40:11 +0100 Message-Id: <1415104811-28142-1-git-send-email-vkuznets@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When build with Debug the following crash is sometimes observed: Call Trace: [] string+0x40/0x100 [] vsnprintf+0x218/0x5e0 [] ? trace_hardirqs_off+0xd/0x10 [] vscnprintf+0x11/0x30 [] vprintk+0xd0/0x5c0 [] ? vmbus_process_rescind_offer+0x0/0x110 [hv_vmbus] [] printk+0x41/0x45 [] vmbus_device_unregister+0x2c/0x40 [hv_vmbus] [] vmbus_process_rescind_offer+0x2b/0x110 [hv_vmbus] ... This happens due to the following race: between 'if (channel->device_obj)' check in vmbus_process_rescind_offer() and pr_debug() in vmbus_device_unregister() the device can disappear. Fix the issue by taking an additional reference to the device before proceeding to vmbus_device_unregister(). Signed-off-by: Vitaly Kuznetsov --- drivers/hv/channel_mgmt.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index a2d1a96..d36ce68 100644 --- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -216,9 +216,16 @@ static void vmbus_process_rescind_offer(struct work_struct *work) unsigned long flags; struct vmbus_channel *primary_channel; struct vmbus_channel_relid_released msg; + struct device *dev; + + if (channel->device_obj) { + dev = get_device(&channel->device_obj->device); + if (dev) { + vmbus_device_unregister(channel->device_obj); + put_device(dev); + } + } - if (channel->device_obj) - vmbus_device_unregister(channel->device_obj); memset(&msg, 0, sizeof(struct vmbus_channel_relid_released)); msg.child_relid = channel->offermsg.child_relid; msg.header.msgtype = CHANNELMSG_RELID_RELEASED; -- 1.9.3