[PATCH] drm: Release spinlock for calling lastclose() after 58474713

[Dave Airlie]

On Sat, Aug 7, 2010 at 10:49 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> When removing of the BKL the locking around lastclose() was rearranged
> and resulted in the holding of the open_count spinlock over the call
> into drm_lastclose(). The drivers were not ready for this path to be
> atomic - it may indeed involve long waits to release old objects and
> cleanup the GPU - and so we ended up scheduling whilst atomic.

I might be missing something, but what stops the race with something
reopening while we are in lastclose now?

Dave.

>
> [   54.625598] BUG: scheduling while atomic: X/3546/0x00000002
> [   54.625600] Modules linked in: sco bridge stp llc input_polldev rfcomm bnep l2cap crc16 sch_sfq ipv6 md_mod acpi_cpufreq mperf cryptd aes_x86_64 aes_generic xts gf128mul dm_crypt dm_mod btusb bluetooth usbhid hid zaurus cdc_ether usbnet mii cdc_wdm cdc_acm uvcvideo videodev v4l1_compat v4l2_compat_ioctl32 snd_hda_codec_conexant arc4 pcmcia ecb snd_hda_intel joydev sdhci_pci sdhci snd_hda_codec tpm_tis firewire_ohci mmc_core e1000e uhci_hcd thinkpad_acpi nvram yenta_socket pcmcia_rsrc pcmcia_core tpm wmi sr_mod firewire_core iwlagn ehci_hcd snd_hwdep snd_pcm usbcore tpm_bios thermal led_class snd_timer iwlcore snd soundcore ac snd_page_alloc pcspkr psmouse serio_raw battery sg mac80211 evdev cfg80211 i2c_i801 iTCO_wdt iTCO_vendor_support cdrom processor crc_itu_t rfkill xfs exportfs sd_mod crc_t10dif ahci libahci libata scsi_mod [last unloaded: scsi_wait_scan]
> [   54.625663] Pid: 3546, comm: X Not tainted 2.6.35-04771-g1787985 #301
> [   54.625665] Call Trace:
> [   54.625671]  [<ffffffff8102d599>] __schedule_bug+0x57/0x5c
> [   54.625675]  [<ffffffff81384141>] schedule+0xe5/0x832
> [   54.625679]  [<ffffffff81163e77>] ? put_dec+0x20/0x3c
> [   54.625682]  [<ffffffff81384dd4>] schedule_timeout+0x275/0x29f
> [   54.625686]  [<ffffffff810455e1>] ? process_timeout+0x0/0xb
> [   54.625688]  [<ffffffff81384e17>] schedule_timeout_uninterruptible+0x19/0x1b
> [   54.625691]  [<ffffffff81045893>] msleep+0x16/0x1d
> [   54.625695]  [<ffffffff812a2e53>] i9xx_crtc_dpms+0x273/0x2ae
> [   54.625698]  [<ffffffff812a18be>] intel_crtc_dpms+0x28/0xe7
> [   54.625702]  [<ffffffff811ec0fa>] drm_helper_disable_unused_functions+0xf0/0x118
> [   54.625705]  [<ffffffff811ecde3>] drm_crtc_helper_set_config+0x644/0x7c8
> [   54.625708]  [<ffffffff811f12dd>] ? drm_copy_field+0x40/0x50
> [   54.625711]  [<ffffffff811ebca2>] drm_fb_helper_force_kernel_mode+0x3e/0x85
> [   54.625713]  [<ffffffff811ebcf2>] drm_fb_helper_restore+0x9/0x24
> [   54.625717]  [<ffffffff81290a41>] i915_driver_lastclose+0x2b/0x5c
> [   54.625720]  [<ffffffff811f14a7>] drm_lastclose+0x44/0x2ad
> [   54.625722]  [<ffffffff811f1ed2>] drm_release+0x5c6/0x609
> [   54.625726]  [<ffffffff810d1275>] fput+0x109/0x1c7
> [   54.625728]  [<ffffffff810ce5e4>] filp_close+0x61/0x6b
> [   54.625731]  [<ffffffff810ce680>] sys_close+0x92/0xd4
> [   54.625734]  [<ffffffff81002a2b>] system_call_fastpath+0x16/0x1b
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/drm_fops.c |    9 ++++-----
>  1 files changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> index 2ca8df8..6367961 100644
> --- a/drivers/gpu/drm/drm_fops.c
> +++ b/drivers/gpu/drm/drm_fops.c
> @@ -572,16 +572,15 @@ int drm_release(struct inode *inode, struct file *filp)
>        atomic_inc(&dev->counts[_DRM_STAT_CLOSES]);
>        spin_lock(&dev->count_lock);
>        if (!--dev->open_count) {
> +               spin_unlock(&dev->count_lock);
> +
>                if (atomic_read(&dev->ioctl_count)) {
>                        DRM_ERROR("Device busy: %d\n",
>                                  atomic_read(&dev->ioctl_count));
>                        retcode = -EBUSY;
> -                       goto out;
> -               }
> -               retcode = drm_lastclose(dev);
> +               } else
> +                       retcode = drm_lastclose(dev);
>        }
> -out:
> -       spin_unlock(&dev->count_lock);
>        mutex_unlock(&drm_global_mutex);
>
>        return retcode;
> --
> 1.7.1
>
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