Messages in this thread | | | Date | Thu, 13 May 2010 01:58:14 +0200 | From | Andrej Gelenberg <> | Subject | Re: [PATCH] [CPUFREQ] fix race condition in store_scaling_governor |
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Hi,
On 05/13/2010 12:00 AM, Andrew Morton wrote: > > Looks sane, I guess. > > I am afraid of moving all those functions inside > cpufreq_governor_mutex. Not for any specific reason, apart from a long > history of nasty deadlocks with cpufreq global locks :( > > Has this change been well-tested with lockdep enabled?
It prevent at least the kernel panic and warnings from sysfs, but cause a deadlock. I can confirm the bug in 2.6.33-ARCH (last stable kernel in archlinux):
------------[ cut here ]------------ WARNING: at fs/sysfs/dir.c:487 sysfs_add_one+0xc5/0x150() Hardware name: 287655G sysfs: cannot create duplicate filename '/devices/system/cpu/cpu0/cpufreq/ondemand' Modules linked in: cpufreq_conservative cpufreq_ondemand powernow_k8 freq_table joydev radeon ttm drm_kms_helper snd_seq_dummy uvcvideo drm videodev rfkill i2c_algo_bit snd_seq_oss v4l1_compat usb_storage v4l2_compat_ioctl32 snd_seq_midi_event led_class snd_seq snd_seq_device nvram snd_hda_codec_conexant snd_hda_intel video snd_pcm_oss snd_mixer_oss output snd_hda_codec snd_hwdep snd_pcm snd_timer snd ohci_hcd soundcore shpchp ehci_hcd ac wmi battery sg thermal processor button snd_page_alloc psmouse i2c_piix4 edac_core pci_hotplug r8169 usbcore mii edac_mce_amd serio_raw i2c_core k8temp evdev pcspkr rtc_cmos rtc_core rtc_lib ext4 mbcache jbd2 crc16 cryptd aes_x86_64 aes_generic xts gf128mul dm_crypt dm_mod sd_mod ahci libata scsi_mod Pid: 3136, comm: test_cpu.sh Tainted: G W 2.6.33-ARCH #1 Call Trace: [<ffffffff810529f6>] warn_slowpath_common+0x76/0xb0 [<ffffffff81052a8c>] warn_slowpath_fmt+0x3c/0x40 [<ffffffff81187f45>] sysfs_add_one+0xc5/0x150 [<ffffffff81188033>] create_dir+0x63/0xc0 [<ffffffff811880a6>] sysfs_create_subdir+0x16/0x20 [<ffffffff8118950a>] internal_create_group+0x5a/0x190 [<ffffffff8118966e>] sysfs_create_group+0xe/0x10 [<ffffffffa056fcfc>] cpufreq_governor_dbs+0xac/0x3e0 [cpufreq_ondemand] [<ffffffff810788bd>] ? notifier_call_chain+0x4d/0x70 [<ffffffff81293f25>] __cpufreq_governor+0xf5/0x1e0 [<ffffffff812954ec>] __cpufreq_set_policy+0x13c/0x180 [<ffffffff812958f8>] store_scaling_governor+0xe8/0x220 [<ffffffff81296240>] ? handle_update+0x0/0x10 [<ffffffff811cb7ba>] ? kobject_get+0x1a/0x30 [<ffffffff81295382>] store+0x62/0x90 [<ffffffff81186820>] sysfs_write_file+0xe0/0x160 [<ffffffff81121576>] vfs_write+0xb6/0x190 [<ffffffff8103175d>] ? do_page_fault+0x15d/0x320 [<ffffffff811218ac>] sys_write+0x4c/0x80 [<ffffffff81009f02>] system_call_fastpath+0x16/0x1b ---[ end trace 939cd7811bc2accf ]---
Here is my test script:
#!/bin/sh for k in {1..4} do for i in conservative ondemand performance do echo $i > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor & done done
for k in {1..4} do for i in conservative ondemand performance do echo $i > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor & done done echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
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