Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758725AbYFXJRS (ORCPT ); Tue, 24 Jun 2008 05:17:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750751AbYFXJRH (ORCPT ); Tue, 24 Jun 2008 05:17:07 -0400 Received: from E23SMTP03.au.ibm.com ([202.81.18.172]:39492 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751130AbYFXJRF (ORCPT ); Tue, 24 Jun 2008 05:17:05 -0400 Message-ID: <4860BB8E.2070505@linux.vnet.ibm.com> Date: Tue, 24 Jun 2008 14:47:02 +0530 From: Nageswara R Sastry User-Agent: Thunderbird 2.0.0.14 (X11/20080505) MIME-Version: 1.0 To: Johannes Weiner CC: linux-kernel@vger.kernel.org, balbir@linux.vnet.ibm.com, ego@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com, davej@codemonkey.org.uk Subject: Re: [BUG] While changing the cpufreq governor, kernel hits a bug in workqueue.c References: <485F8028.1070302@linux.vnet.ibm.com> <87y74w41fp.fsf@skyscraper.fehenstaub.lan> In-Reply-To: <87y74w41fp.fsf@skyscraper.fehenstaub.lan> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5808 Lines: 148 Johannes Weiner wrote: > > From: Johannes Weiner > Subject: cpufreq: Fix race in enabling ondemand/conservative governors > > Prevent double activation of the governor if two processes race on the > check for whether the governor is already active. > > Signed-off-by: Johannes Weiner > --- > > diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c > index 5d3a04b..a4902e4 100644 > --- a/drivers/cpufreq/cpufreq_conservative.c > +++ b/drivers/cpufreq/cpufreq_conservative.c > @@ -486,10 +486,11 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, > if ((!cpu_online(cpu)) || (!policy->cur)) > return -EINVAL; > > - if (this_dbs_info->enable) /* Already enabled */ > - break; > - > mutex_lock(&dbs_mutex); > + if (this_dbs_info->enable) { > + mutex_unlock(&dbs_mutex); > + break; > + } > > rc = sysfs_create_group(&policy->kobj, &dbs_attr_group); > if (rc) { > diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c > index d2af20d..61705e1 100644 > --- a/drivers/cpufreq/cpufreq_ondemand.c > +++ b/drivers/cpufreq/cpufreq_ondemand.c > @@ -508,10 +508,12 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, > if ((!cpu_online(cpu)) || (!policy->cur)) > return -EINVAL; > > - if (this_dbs_info->enable) /* Already enabled */ > + mutex_lock(&dbs_mutex); > + if (this_dbs_info->enable) { > + mutex_unlock(&dbs_mutex); > break; > + } > > - mutex_lock(&dbs_mutex); > dbs_enable++; > > rc = sysfs_create_group(&policy->kobj, &dbs_attr_group); Applied the above patch against 2.6.25.7 kernel and tested the same, But unluckily the above patch didn't stop hitting kernel bug at kernel/workqueue.c:223 Hitting bug time got delayed near to 2hrs with the above patch. >> Kernel stack trace: ------------[ cut here ]------------ kernel BUG at kernel/workqueue.c:223! invalid opcode: 0000 [#2] SMP Modules linked in: cpufreq_powersave cpufreq_conservative cpufreq_userspace usbhid usb_storage ehci_hcd ohci_hcd uhci_hcd usbcore Pid: 232, comm: kondemand/1 Tainted: G D (2.6.25.7.cpufreqpatch #2) EIP: 0060:[] EFLAGS: 00010286 CPU: 1 EIP is at queue_delayed_work_on+0x20/0x97 EAX: 00000000 EBX: c483ba94 ECX: c483ba94 EDX: 00000000 ESI: c483bab0 EDI: f7a39708 EBP: 00000001 ESP: f7a69f40 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 Process kondemand/1 (pid: 232, ti=f7a68000 task=f79b4120 task.ti=f7a68000) Stack: 00000000 f7a377b0 c483ba80 f78bed80 c041e54d 00000040 00000000 00000001 00000040 00000246 00000000 00000002 00000000 c012ee7f c483ba98 f7a377b0 c483ba94 f7a69f9c c012eeba 00000000 00000002 c012ee7f c041e31e c099e2a8 Call Trace: [] do_dbs_timer+0x22f/0x24f [] run_workqueue+0x81/0x187 [] run_workqueue+0xbc/0x187 [] run_workqueue+0x81/0x187 [] do_dbs_timer+0x0/0x24f [] worker_thread+0x0/0xbd [] worker_thread+0xb3/0xbd [] autoremove_wake_function+0x0/0x2d [] kthread+0x38/0x5d [] kthread+0x0/0x5d [] kernel_thread_helper+0x7/0x10 ======================= Code: c3 a1 dc da 6a c0 e9 78 ff ff ff 55 89 c5 57 89 d7 56 53 89 cb 8d 71 1c f0 0f ba 29 00 19 c0 31 d2 85 c0 75 76 83 79 1c 00 74 04 <0f> 0b eb fe 8d 41 04 39 41 04 74 04 0f 0b eb fe 89 f8 64 8b 15 EIP: [] queue_delayed_work_on+0x20/0x97 SS:ESP 0068:f7a69f40 ---[ end trace 1f82bd8b1ee896cc ]--- And when the script is running opened one more terminal and issued the following command to observe the state of governors. # watch -n 1 "cat /proc/cpuinfo | grep 'cpu MHz' ; cat /proc/acpi/processor/CPU*/performance; cat /sys/devices/system/cpu/*/cpufreq/scaling_governor; cat /sys/devices/system/cpu/*/cpufreq/scaling_cur_freq" The above command hit with an another kernel BUG at kernel/workqueue.c:272 the kernel stack trace is, ------------[ cut here ]------------ kernel BUG at kernel/workqueue.c:272! invalid opcode: 0000 [#1] SMP Modules linked in: cpufreq_powersave cpufreq_conservative cpufreq_userspace usbhid usb_storage ehci_hcd ohci_hcd uhci_hcd usbcore Pid: 233, comm: kondemand/2 Not tainted (2.6.25.7.cpufreqpatch #2) EIP: 0060:[] EFLAGS: 00010212 CPU: 2 EIP is at run_workqueue+0x7d/0x187 EAX: f7a377b0 EBX: c4844a98 ECX: 00000000 EDX: 00000000 ESI: f7a37718 EDI: c4844a94 EBP: f79f9f9c ESP: f79f9f98 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 Process kondemand/2 (pid: 233, ti=f79f8000 task=f79b5020 task.ti=f79f8000) Stack: c041e31e c099e2a8 00000000 c061ec35 f7a37718 c012f6fa f7a3773c 00000000 c012f7ad 00000000 f79b5020 c0131acc f79f9fc8 f79f9fc8 f7a37718 00000000 c0131a1b c01319e3 00000000 c0105527 f784bef0 00000000 00000000 00000000 Call Trace: [] do_dbs_timer+0x0/0x24f [] worker_thread+0x0/0xbd [] worker_thread+0xb3/0xbd [] autoremove_wake_function+0x0/0x2d [] kthread+0x38/0x5d [] kthread+0x0/0x5d [] kernel_thread_helper+0x7/0x10 ======================= Code: e8 d3 2f 16 00 8b 46 1c 89 7e 48 8b 08 8b 50 04 89 51 04 89 0a 89 40 04 89 00 89 f0 e8 59 ff 39 00 8b 43 fc 83 e0 fc 39 f0 74 04 <0f> 0b eb fe f0 0f ba 73 fc 00 8b 46 4c 31 c9 31 d2 68 7f ee 12 EIP: [] run_workqueue+0x7d/0x187 SS:ESP 0068:f79f9f98 ---[ end trace 1f82bd8b1ee896cc ]--- Regards R.Nageswara Sastry, CSTE, CEH, CSTM Linux Technology Center IBM India System & Technology Lab -- 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/