linux-kernel - RE: 2.6.30-rc2 hangs in get_measured

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Date:	Wed, 15 Apr 2009 06:31:45 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Denis Sadykov <denis.m.sadykov@...el.com>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: 2.6.30-rc2 hangs in get_measured_perf on tigerton

 

>-----Original Message-----
>From: cpufreq-owner@...r.kernel.org 
>[mailto:cpufreq-owner@...r.kernel.org] On Behalf Of Rusty Russell
>Sent: Wednesday, April 15, 2009 4:14 AM
>To: Zhang, Yanmin
>Cc: LKML; Pallipadi, Venkatesh; Denis Sadykov; 
>cpufreq@...r.kernel.org; linux-acpi@...r.kernel.org
>Subject: Re: 2.6.30-rc2 hangs in get_measured_perf on tigerton
>
>On Wed, 15 Apr 2009 03:31:23 pm Zhang, Yanmin wrote:
>> My machine hanged with kernel 2.6.30-rc2 when script read
>> /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor.
>> 
>> opps happens in get_measured_perf:
>> 
>>         cur.aperf.whole = readin.aperf.whole -
>>                                 per_cpu(drv_data, cpu)->saved_aperf;
>> 
>> Because per_cpu(drv_data, cpu)=NULL.
>> 
>> So function get_measured_perf should check if 
>(per_cpu(drv_data, cpu)==NULL)
>> and return 0 if it's NULL.
>> 
>> Other functions have such checking.
>
>Possibly true, but I can't see that get_measured_perf() ever did.
>
>Unless there's something subtle with preemption no longer 
>being disabled
>inside that function...
>

Checking the NULL and returning is not an option. We need to
look at average current freq on all CPUs to make correct
next freq decision. Also, per_cpu drv_data should be set
for all CPUs. I will poke a bit at this and get back...

Thanks,
Venki


>> 
>> 
>> --------------sys log------------------
>> 
>> BUG: unable to handle kernel NULL pointer dereference at 
>0000000000000020
>> IP: [<ffffffff8021af75>] get_measured_perf+0x4a/0xf9
>> PGD a7dd88067 PUD a7ccf5067 PMD 0 
>> Oops: 0000 [#1] SMP 
>> last sysfs file: 
>/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
>> CPU 0 
>> Modules linked in: video output
>> Pid: 2091, comm: kondemand/0 Not tainted 2.6.30-rc2 #1 MP Server
>> RIP: 0010:[<ffffffff8021af75>]  [<ffffffff8021af75>] 
>get_measured_perf+0x4a/0xf9
>> RSP: 0018:ffff880a7d56de20  EFLAGS: 00010246
>> RAX: 0000000000000000 RBX: 00000046241a42b6 RCX: ffff88004d219000
>> RDX: 000000000000b660 RSI: 0000000000000020 RDI: 0000000000000001
>> RBP: ffff880a7f052000 R08: 00000046241a42b6 R09: ffffffff807639f0
>> R10: 00000000ffffffea R11: ffffffff802207f4 R12: ffff880a7f052000
>> R13: ffff88004d20e460 R14: 0000000000ddd5a6 R15: 0000000000000001
>> FS:  0000000000000000(0000) GS:ffff88004d200000(0000) 
>knlGS:0000000000000000
>> CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
>> CR2: 0000000000000020 CR3: 0000000a7f1bf000 CR4: 00000000000006e0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>> Process kondemand/0 (pid: 2091, threadinfo ffff880a7d56c000, 
>task ffff880a7d4d18c0)
>> Stack:
>>  ffff880a7f052078 ffffffff803efd54 00000046241a42b6 000000462ffa9e95
>>  0000000000000001 0000000000000001 00000000ffffffea ffffffff8064f41a
>>  0000000000000012 0000000000000012 ffff880a7f052000 ffffffff80650547
>> Call Trace:
>>  [<ffffffff803efd54>] ? kobject_get+0x12/0x17
>>  [<ffffffff8064f41a>] ? __cpufreq_driver_getavg+0x42/0x57
>>  [<ffffffff80650547>] ? do_dbs_timer+0x147/0x272
>>  [<ffffffff80650400>] ? do_dbs_timer+0x0/0x272
>>  [<ffffffff802474ca>] ? worker_thread+0x15b/0x1f5
>>  [<ffffffff8024a02c>] ? autoremove_wake_function+0x0/0x2e
>>  [<ffffffff8024736f>] ? worker_thread+0x0/0x1f5
>>  [<ffffffff80249f0d>] ? kthread+0x54/0x83
>>  [<ffffffff8020c87a>] ? child_rip+0xa/0x20
>>  [<ffffffff80249eb9>] ? kthread+0x0/0x83
>>  [<ffffffff8020c870>] ? child_rip+0x0/0x20
>> Code: 99 a6 03 00 31 c9 85 c0 0f 85 c3 00 00 00 89 df 4c 8b 
>44 24 10 48 c7 c2 60 b6 00 00 48 8b 0c fd e0 30 a5 80 4c 89 c3 
>48 8b 04 0a <48> 2b 58 20 48 8b 44 24 18 48 89 1c 24 48 8b 34 
>0a 48 2b 46 28 
>> RIP  [<ffffffff8021af75>] get_measured_perf+0x4a/0xf9
>>  RSP <ffff880a7d56de20>
>> CR2: 0000000000000020
>> ---[ end trace 2b8fac9a49e19ad4 ]---
>> 
>> 
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