Message-ID: <20090413205908.GA15435@linux.vnet.ibm.com>
Date:	Mon, 13 Apr 2009 13:59:08 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Luis Henriques <henrix@...o.pt>
Cc:	Dave Jones <davej@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	mark.langsdorf@....com, linux-kernel@...r.kernel.org
Subject: Re: [BUG -tip] unable to handle kernel paging request

On Mon, Apr 13, 2009 at 05:59:13PM +0100, Luis Henriques wrote:
> Hi,
> 
> (not sure if I'm CC'ing all the relevant persons...)
> 
> I am hitting this bug, which occurs mainly when I am shutting down my laptop.  I
> took a look at the cpufreq code and found out something which I am not sure if it
> is related with this bug (or even if it is an issue at all):
> 
> void cpufreq_notify_transition(struct cpufreq_freqs *freqs, unsigned int state)
> {
>         struct cpufreq_policy *policy;
> 
>         BUG_ON(irqs_disabled());
> 
>         freqs->flags = cpufreq_driver->flags;
> 
> 		...
> 
> This code accesses cpufreq_driver without using the cpufreq_driver_lock.  I
> believe this is the only place in the code where this lock is not obtaining
> before accessing the global cpufreq_driver.
> 
> Any ideas?

Well, one thought would be that SRCU is protecting it, but when I look
at the code, SRCU is instead only protecting the notifier chain itself.
So SRCU is -not- a substitute for cpufreq_driver_lock in this case.

But the "freqs" argument looks to be a parameter block private to the
caller, so the modification of freqs->old is safe.  Ditto for
adjust_jiffies().

This does use per-CPU data, but it is not clear to me how preemption is
disabled -- or that it is always operating on the current CPU, for that
matter.  And the few notifier callbacks I looked at did not have any
locking either.

So is the cpufreq_driver_lock acquired at a higher level, for example,
by the guy who calls through the cpufreq_driver control blocks?

							Thanx, Paul

> --
> Luis Henriques
> 
> [ 2015.908598] BUG: unable to handle kernel paging request at 0000737463656a6f
> [ 2015.908606] IP: [<0000737463656a6f>] 0x737463656a6f
> [ 2015.908616] PGD 0 
> [ 2015.908620] Oops: 0010 [#1] PREEMPT SMP 
> [ 2015.908627] last sysfs file: /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
> [ 2015.908631] CPU 0 
> [ 2015.908635] Modules linked in: ipv6 powernow_k8 cpufreq_stats af_packet cpufreq_conservative cpufreq_ondemand freq_table cpufreq_powersave cpufreq_userspace sbp2 loop snd_hda_codec_atihdmi snd_hda_codec_realtek rfkill snd_hda_intel ath5k backlight snd_hda_codec evdev i2c_piix4 psmouse k8temp snd_hwdep snd_pcm snd_timer led_class snd_page_alloc input_polldev battery processor ac button sg sr_mod cdrom ata_generic pata_acpi sd_mod ohci_hcd ohci1394 ieee1394 pata_atiixp ahci libata ide_pci_generic ehci_hcd r8169 mii scsi_mod usbcore ide_core thermal fan [last unloaded: kvm]
> [ 2015.908723] Pid: 3117, comm: powernowd Tainted: G   M       2.6.30-rc1-tip-01567-gacf5b32 #19 Satellite A210
> [ 2015.908727] RIP: 0010:[<0000737463656a6f>]  [<0000737463656a6f>] 0x737463656a6f
> [ 2015.908734] RSP: 0018:ffff88007b4ffcd0  EFLAGS: 00010282
> [ 2015.908737] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffffa03957b0
> [ 2015.908740] RDX: ffff88007b4ffdb8 RSI: 0000000000000000 RDI: ffffffffa03957b0
> [ 2015.908744] RBP: ffff88007b4ffd08 R08: 0000000000000000 R09: 0000000000000000
> [ 2015.908747] R10: ffffffff80274269 R11: 0000000000000000 R12: 00000000fffffffd
> [ 2015.908750] R13: 0000000000000000 R14: ffff88007b4ffdb8 R15: 0000000000000000
> [ 2015.908755] FS:  00007f327af266f0(0000) GS:ffff880001042000(0000) knlGS:00000000f6b24720
> [ 2015.908758] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 2015.908762] CR2: 0000737463656a6f CR3: 000000007a4ca000 CR4: 00000000000006e0
> [ 2015.908765] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 2015.908769] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 2015.908772] Process powernowd (pid: 3117, threadinfo ffff88007b4fe000, task ffff88007d864020)
> [ 2015.908776] Stack:
> [ 2015.908778]  ffffffff8027465f ffff88007b4ffcf8 ffffffff810113a0 0000000000000000
> [ 2015.908786]  00000000ffffffff ffffffff81011318 0000000000000000 ffff88007b4ffd58
> [ 2015.908795]  ffffffff8027480e 0000000000000000 ffff88007b4ffdb8 0000000000000000
> [ 2015.908805] Call Trace:
> [ 2015.908808]  [<ffffffff8027465f>] ? notifier_call_chain+0x3f/0x80
> [ 2015.908817]  [<ffffffff8027480e>] __srcu_notifier_call_chain+0x5e/0x90
> [ 2015.908824]  [<ffffffff80274856>] srcu_notifier_call_chain+0x16/0x20
> [ 2015.908830]  [<ffffffff804988a9>] cpufreq_notify_transition+0x89/0xd0
> [ 2015.908837]  [<ffffffffa030da05>] powernowk8_target+0x285/0x7c0 [powernow_k8]
> [ 2015.908845]  [<ffffffffa02da072>] ? cpufreq_set+0x32/0xc0 [cpufreq_userspace]
> [ 2015.908852]  [<ffffffff8049862c>] __cpufreq_driver_target+0x3c/0x40
> [ 2015.908858]  [<ffffffffa02da0ce>] cpufreq_set+0x8e/0xc0 [cpufreq_userspace]
> [ 2015.908865]  [<ffffffff80498bbd>] store_scaling_setspeed+0x6d/0x80
> [ 2015.908871]  [<ffffffff8049a66f>] store+0x6f/0xa0
> [ 2015.908876]  [<ffffffff8037a54f>] sysfs_write_file+0xcf/0x140
> [ 2015.908883]  [<ffffffff80318b4b>] vfs_write+0xcb/0x170
> [ 2015.908889]  [<ffffffff80318ce5>] sys_write+0x55/0x90
> [ 2015.908895]  [<ffffffff8020c1f2>] system_call_fastpath+0x16/0x1b
> [ 2015.908902] Code:  Bad RIP value.
> [ 2015.908907] RIP  [<0000737463656a6f>] 0x737463656a6f
> [ 2015.908913]  RSP <ffff88007b4ffcd0>
> [ 2015.908915] CR2: 0000737463656a6f
> [ 2015.909459] ---[ end trace cefb79d041e94864 ]---
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