On Thu, May 13, 2010 at 01:58:14AM +0200, Andrej Gelenberg wrote: >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): > Well, this is not a panic, it is just a WARNING. >------------[ 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 ]--- > Hmm, so two processes enter store_scaling_governor() at the same time, one will enter mutex_lock(&dbs_mutex); while the other one is blocking, when that one leaves mutex_unlock(&dbs_mutex), the other one enters. Yeah, makes sense, but I am still not sure if we could reuse this cpufreq_governor_mutex... Thanks. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
