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    SubjectRe: [PATCH 2.6.27-rc8 5/6] e1000e: debug contention on NVM SWFLAG
    On Thu, 2 Oct 2008, Jesse Brandeburg wrote:

    > From: Thomas Gleixner <tglx@linutronix.de>
    >
    > This patch adds a mutex to the e1000e driver that would help
    > catch any collisions of two e1000e threads accessing hardware
    > at the same time.

    Apparently this has some bug wrt suspend, see
    https://bugzilla.novell.com/show_bug.cgi?id=431914

    WARNING: at drivers/net/e1000e/ich8lan.c:424
    e1000_acquire_swflag_ich8lan+0x56/0xcb [e1000e]()
    e1000e mutex contention. Owned by pid -1
    Modules linked in: xt_tcpudp xt_pkttype tun ipt_ULOG xt_limit aes_i586
    aes_generic i915 drm af_packet snd_pcm_oss snd_mixer_oss snd_seq
    snd_seq_device ipt_REJECT xt_state cpufreq_conservative iptable_mangle
    cpufreq_userspace iptable_nat cpufreq_powersave nf_nat acpi_cpufreq
    iptable_filter speedstep_lib nf_conntrack_ipv4 nf_conntrack ip_tables
    ip6_tables x_tables microcode loop arc4 ecb crypto_blkcipher snd_hda_intel
    iwl3945 pcmcia thinkpad_acpi snd_pcm snd_timer sdhci_pci snd_page_alloc
    rfkill sdhci snd_hwdep mac80211 yenta_socket rsrc_nonstatic video rtc_cmos
    led_class ohci1394 snd ieee1394 output mmc_core i2c_i801 ac battery
    pcmcia_core iTCO_wdt button intel_agp rtc_core cfg80211 nvram soundcore
    iTCO_vendor_support agpgart e1000e rtc_lib i2c_core pcspkr uinput sg
    sd_mod ehci_hcd uhci_hcd crc_t10dif usbcore edd ext3 mbcache jbd fan
    ata_piix ahci libata scsi_mod dock thermal processor
    Pid: 23153, comm: events/1 Tainted: G W
    2.6.27-rc8-HEAD_20081001123454-pae #1
    [<c0105590>] dump_trace+0x6b/0x249
    [<c01060c5>] show_trace+0x20/0x39
    [<c033b52d>] dump_stack+0x71/0x76
    [<c012ba12>] warn_slowpath+0x6f/0x90
    [<f91cfb9b>] e1000_acquire_swflag_ich8lan+0x56/0xcb [e1000e]
    [<f91d3db4>] e1000e_read_phy_reg_igp+0x10/0x4f [e1000e]
    [<f91d3f83>] e1000e_phy_has_link_generic+0x32/0x99 [e1000e]
    [<f91d2e35>] e1000e_check_for_copper_link+0x26/0x80 [e1000e]
    [<f91d8f3a>] e1000_watchdog_task+0x5b/0x5eb [e1000e]
    [<c013a1b4>] run_workqueue+0x9f/0x13e
    [<c013a309>] worker_thread+0xb6/0xc2
    [<c013cdff>] kthread+0x38/0x5d
    [<c01050e7>] kernel_thread_helper+0x7/0x10

    > + WARN_ON(preempt_count());
    > +
    > + if (!mutex_trylock(&nvm_mutex)) {
    > + WARN(1, KERN_ERR "e1000e mutex contention. Owned by pid %d\n",
    > + nvm_owner);
    > + mutex_lock(&nvm_mutex);
    > + }
    > + nvm_owner = current->pid;
    > +
    > while (timeout) {
    > extcnf_ctrl = er32(EXTCNF_CTRL);
    > extcnf_ctrl |= E1000_EXTCNF_CTRL_SWFLAG;
    > @@ -407,6 +419,8 @@ static s32 e1000_acquire_swflag_ich8lan(struct e1000_hw *hw)
    >
    > if (!timeout) {
    > hw_dbg(hw, "FW or HW has locked the resource for too long.\n");
    > + nvm_owner = -1;
    > + mutex_unlock(&nvm_mutex);
    > return -E1000_ERR_CONFIG;
    > }
    >
    > @@ -428,6 +442,9 @@ static void e1000_release_swflag_ich8lan(struct e1000_hw *hw)
    > extcnf_ctrl = er32(EXTCNF_CTRL);
    > extcnf_ctrl &= ~E1000_EXTCNF_CTRL_SWFLAG;
    > ew32(EXTCNF_CTRL, extcnf_ctrl);
    > +
    > + nvm_owner = -1;
    > + mutex_unlock(&nvm_mutex);
    > }

    The debugging message is racy anyway with respect to accessing nvm_owner,
    right? It should be done after the mutex has been succesfully acquired.

    --
    Jiri Kosina
    SUSE Labs



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