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

Mauro Carvalho Chehab
2015-11-16T18:37:01Z

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