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    SubjectRe: [PATCH] [CPUFREQ] fix race condition in store_scaling_governor
    On Thu, May 13, 2010 at 01:58:14AM +0200, Andrej Gelenberg wrote:
    >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
    >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: 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...


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      Last update: 2010-05-13 11:11    [W:0.040 / U:3.844 seconds]
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