Re: [PATCH] media: fix kernel hang in media_device_unregister() during device removal

[Mauro Carvalho Chehab <mchehab@osg.samsung.com>]

Em Mon, 16 Nov 2015 01:02:56 +0200
Sakari Ailus <sakari.ailus@iki.fi> escreveu:

> Hi Shuah,
> 
> On Thu, Nov 12, 2015 at 07:41:47AM -0700, Shuah Khan wrote:
> > Media core drivers (dvb, v4l2, bridge driver) unregister
> > their entities calling media_device_unregister_entity()
> > during device removal from their unregister paths. In
> > addition media_device_unregister() tries to unregister
> > entity calling media_device_unregister_entity() for each
> > one of them. This adds lot of contention on mdev->lock in
> > device removal sequence. Fix to not unregister entities
> > from media_device_unregister(), and let drivers take care
> > of it. Drivers need to unregister to cover the case of
> > module removal. This patch fixes the problem by deleting
> > the entity list walk to call media_device_unregister_entity()
> > for each entity. With this fix there is no kernel hang after
> > a sequence of device insertions followed by removal.
> > 
> > Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
> > ---
> >  drivers/media/media-device.c | 5 -----
> >  1 file changed, 5 deletions(-)
> > 
> > diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> > index 1312e93..c7ab7c9 100644
> > --- a/drivers/media/media-device.c
> > +++ b/drivers/media/media-device.c
> > @@ -577,8 +577,6 @@ EXPORT_SYMBOL_GPL(__media_device_register);
> >   */
> >  void media_device_unregister(struct media_device *mdev)
> >  {
> > -	struct media_entity *entity;
> > -	struct media_entity *next;
> >  	struct media_link *link, *tmp_link;
> >  	struct media_interface *intf, *tmp_intf;
> >  
> > @@ -596,9 +594,6 @@ void media_device_unregister(struct media_device *mdev)
> >  		kfree(intf);
> >  	}
> >  
> > -	list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
> > -		media_device_unregister_entity(entity);
> > -
> >  	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
> >  	media_devnode_unregister(&mdev->devnode);
> >  
> 
> media_device_unregister() is expected to clean up all the entities still
> registered with it (as it does to links and interfaces). Could you share
> details of the problems you saw in case you haven't found the actual
> underlying issue causing them?
> 

I was not able to reproduce here with au0828. Tried to register/unregister 20
times with:
	$ i=1; while :; do echo $i; sudo modprobe au0828 && sleep 2 && sudo rmmod au0828; i=$((i+1)); done

The results are at:
	http://pastebin.com/1B9c9nYm


PS.: I had to add the 2 seconds sleep there, as otherwise unregister may
fail, because udev is started every time the devnodes are created. Without
that, sometimes it returns -EBUSY, because udev didn't close the devnode
yet. Still no problem, as a later rmmod works:

	$ sudo modprobe au0828 && sudo rmmod au0828
	$ sudo modprobe au0828 && sudo rmmod au0828
	rmmod: ERROR: Module au0828 is in use
	$  sudo rmmod au0828
	$ 

So, I don't think that the issues you're experiencing are related to the
MC next generation. 

As a reference, those are the modules I'm using on my test machine
(after removing the remaining media modules):

$ lsmod
Module                  Size  Used by
cpufreq_powersave      16384  0
cpufreq_conservative    16384  0
cpufreq_userspace      16384  0
cpufreq_stats          16384  0
parport_pc             28672  0
ppdev                  20480  0
lp                     20480  0
parport                40960  3 lp,ppdev,parport_pc
snd_usb_audio         151552  0
snd_hda_codec_hdmi     53248  1
snd_usbmidi_lib        28672  1 snd_usb_audio
snd_rawmidi            24576  1 snd_usbmidi_lib
snd_seq_device         16384  1 snd_rawmidi
btusb                  40960  0
btrtl                  16384  1 btusb
btbcm                  16384  1 btusb
btintel                16384  1 btusb
bluetooth             434176  5 btbcm,btrtl,btusb,btintel
rfkill                 20480  1 bluetooth
i915                 1110016  4
intel_rapl             20480  0
iosf_mbi               16384  1 intel_rapl
x86_pkg_temp_thermal    16384  0
intel_powerclamp       16384  0
coretemp               16384  0
kvm_intel             163840  0
kvm                   446464  1 kvm_intel
irqbypass              16384  1 kvm
crct10dif_pclmul       16384  0
snd_hda_codec_realtek    65536  1
crc32_pclmul           16384  0
crc32c_intel           24576  0
i2c_algo_bit           16384  1 i915
snd_hda_codec_generic    65536  1 snd_hda_codec_realtek
drm_kms_helper        102400  1 i915
snd_hda_intel          32768  0
snd_hda_codec         102400  4 snd_hda_codec_realtek,snd_hda_codec_hdmi,snd_hda_codec_generic,snd_hda_intel
jitterentropy_rng      16384  0
drm                   278528  5 i915,drm_kms_helper
sha256_ssse3           32768  1
sha256_generic         24576  1 sha256_ssse3
snd_hwdep              16384  2 snd_usb_audio,snd_hda_codec
hmac                   16384  1
snd_hda_core           49152  5 snd_hda_codec_realtek,snd_hda_codec_hdmi,snd_hda_codec_generic,snd_hda_codec,snd_hda_intel
drbg                   24576  1
iTCO_wdt               16384  0
snd_pcm                86016  5 snd_usb_audio,snd_hda_codec_hdmi,snd_hda_codec,snd_hda_intel,snd_hda_core
iTCO_vendor_support    16384  1 iTCO_wdt
evdev                  24576  8
aesni_intel           167936  0
snd_timer              28672  1 snd_pcm
aes_x86_64             20480  1 aesni_intel
psmouse               110592  0
mei_me                 28672  0
lrw                    16384  1 aesni_intel
snd                    57344  12 snd_hda_codec_realtek,snd_usb_audio,snd_hwdep,snd_timer,snd_hda_codec_hdmi,snd_pcm,snd_rawmidi,snd_hda_codec_generic,snd_usbmidi_lib,snd_hda_codec,snd_hda_intel,snd_seq_device
gf128mul               16384  1 lrw
glue_helper            16384  1 aesni_intel
mei                    81920  1 mei_me
ablk_helper            16384  1 aesni_intel
cryptd                 20480  2 aesni_intel,ablk_helper
soundcore              16384  1 snd
serio_raw              16384  0
shpchp                 32768  0
pcspkr                 16384  0
sg                     32768  0
i2c_i801               20480  0
lpc_ich                24576  0
mfd_core               16384  1 lpc_ich
battery                16384  0
i2c_designware_platform    16384  0
i2c_designware_core    20480  1 i2c_designware_platform
dw_dmac                16384  0
tpm_tis                20480  0
video                  32768  1 i915
tpm                    36864  1 tpm_tis
dw_dmac_core           24576  1 dw_dmac
button                 16384  1 i915
acpi_pad               24576  0
ext4                  495616  6
crc16                  16384  2 ext4,bluetooth
mbcache                20480  1 ext4
jbd2                   90112  1 ext4
dm_mod                 98304  18
sd_mod                 40960  3
ahci                   36864  2
libahci                28672  1 ahci
libata                192512  2 ahci,libahci
ehci_pci               16384  0
scsi_mod              192512  3 sg,libata,sd_mod
ehci_hcd               73728  1 ehci_pci
e1000e                208896  0
xhci_pci               16384  0
ptp                    20480  1 e1000e
xhci_hcd              155648  1 xhci_pci
pps_core               16384  1 ptp
fan                    16384  0
thermal                20480  0
sdhci_acpi             16384  0
sdhci                  36864  1 sdhci_acpi
mmc_core              106496  2 sdhci,sdhci_acpi
i2c_hid                20480  0
hid                   110592  1 i2c_hid

A clear difference is that this machine uses the i915 graph driver,
instead of the Radeon driver that you're using on your machine.

So, I still think that the problem you've noticed is related to the
radeon driver. Please test without it, booting the machine on
console mode, in order to isolate eventual issues with the graphics
stack.

Regards,
Mauro