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[Ernst Martin Witte <1532412@xxxxxxxxxxxxxxxxxx>]

patch set submitted to linux-media@xxxxxxxxxxxxxxx:
         [PATCH 0/5] [media] cancel_delayed_work_sync before device removal / kfree

Seems  that the  cause  for the  kernel  panic is  a  missing call  to
cancel_delayed_work_sync in  si2157_remove before  the call  to kfree.
After adding cancel_delayed_work_sync(&dev->stat_work), rmmod does not
trigger the kernel panic any more.

However, very similar issues could be identified also in other modules:

   ts2020
   af9013
   af9033
   rtl2830

when looking in drivers/media/tuners and drivers/media/dvb-frontends.

Therefore,  a patch set has been submitted to linux-media@xxxxxxxxxxxxxxx 
which contains  fixes for  those modules, too. The submitted patch set is:

   [PATCH 0/5] [media] cancel_delayed_work_sync before device removal /
kfree

I hope these patches completely fix the issue and are ok for inclusion
in the kernel.

BR and thx!
  Martin

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https://bugs.launchpad.net/bugs/1532412

Title:
  kernel panic after "rmmod cx23885" by upstream commit 2f1ea29f /
  "[media] si2157: implement signal strength stats"

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  [Reported also on linux-media@xxxxxxxxxxxxxxx]

    * relevance / use-case:

      HTPC going into sleep (currently  requires rmmod as isolated here)
      when not being used.

    * base system:

      - Ubuntu 15.10 (arch: amd64)
      - PCIe DVB-C card DVBSky T982 (2 DVB-C/T tuners)
      - starting point: Ubuntu kernel 4.2.x / x86_64

    * reliably trigger kernel panic (analyzed with kdb / gdb):

     -  run tvheadend  4.x using the  DVB-C tuners (from git/master  in my
        case, but actual release should  not be that relevant) ...  likely
        any other DVB-C application would be sufficient.

      - stop tvheadend

      - rmmod cx23885

        Please note: It seems to be  relevant that the DVB-C tuners were
        in use (and released) before the call to rmmod.  During testing,
        I  had situations  where I  could successfully  do the  rmmod if
        tvheadend was not yet started after a fresh boot.

        The kernel  panic happens  after the rmmod  with a  little delay
        (less than a second) - in some completely unrelated parts of the
        kernel, but reproducible locations, e.g. a stack frame like:

            call_timer_fn+0x35/0xf0
            __run_timers (inlined)
            run_timer_softirq+0x221/0x2d0
            __do_softirq+0x0f6/0250

            (unable to handle paging request, aka invalid pointer)

        or

            call_timer_fn+0x35/0xf0
            __run_timers (inlined)
            run_timer_softirq+0x162/0x2d0
            __do_softirq+0x0f6/0250

            (null pointer dereference)

        The faulting line is a call to NULL or invalid function pointer,
        namely line 1178 in media_tree/kernel/time/timer.c

        1177         trace_timer_expire_entry(timer);
        1178         fn(data);
        1179         trace_timer_expire_exit(timer);

        fn is a  null pointer if called within the  "if (irqsafe)" block
        or an invalid pointer if  called from the respective else branch
        (ll. 1284 in media_tree/kernel/time/timer.c)

    * Affected:

         - v4.2.x

         - v4.3.x

         - v4.4-rcX

    * Not affected: v4.1.x

    * Bisect   result    on   git://github.com/torvalds/linux.git/master
      between v4.1 and v4.2

      2f1ea29fca781b8e6600f3ece1f2dd98ae276294 is the first bad commit
      commit 2f1ea29fca781b8e6600f3ece1f2dd98ae276294
      Author: Antti Palosaari <crope <at> iki.fi>
      Date:   Sun Sep 7 11:20:34 2014 -0300

          [media] si2157: implement signal strength stats

          Implement DVBv5 signal strength stats. Returns dBm.

          Signed-off-by: Antti Palosaari <crope <at> iki.fi>
          Tested-by: Adam Baker <linux <at> baker-net.org.uk>
          Signed-off-by: Mauro Carvalho Chehab <mchehab <at> osg.samsung.com>

      :040000 040000 1fc70a3d18532f91289e8b581081ee59feefc321
  5130e9b011e9c4ba683cd4db3eae8dca67c3ef0e M      drivers

    * Workaround:

      Reverting this patch on my tested kernels (incl. 4.4.rc8) prevents
      the kernel panic.

  BR,
    Martin

  P.S.: Bisect log:

  user <at> host:/a/b/c$ git bisect log
  # bad: [64291f7db5bd8150a74ad2036f1037e6a0428df2] Linux 4.2
  # good: [b953c0d234bc72e8489d3bf51a276c5c4ec85345] Linux 4.1
  git bisect start 'v4.2' 'v4.1'
  # bad: [c11d716218910c3aa2bac1bb641e6086ad649555] Merge tag 'armsoc-cleanup' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
  git bisect bad c11d716218910c3aa2bac1bb641e6086ad649555
  # good: [8a8c35fadfaf55629a37ef1a8ead1b8fb32581d2] mm: kmemleak_alloc_percpu() should follow the
  gfp from per_alloc()
  git bisect good 8a8c35fadfaf55629a37ef1a8ead1b8fb32581d2
  # good: [14738e03312ff1137109d68bcbf103c738af0f4a] Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
  git bisect good 14738e03312ff1137109d68bcbf103c738af0f4a
  # good: [4570a37169d4b44d316f40b2ccc681dc93fedc7b] Merge tag 'sound-4.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
  git bisect good 4570a37169d4b44d316f40b2ccc681dc93fedc7b
  # bad: [78aad7f81aa6dfccdb2804ac35db6fc371d265cf] [media] vivid-tpg: precalculate
  colorspace/xfer_func combinations
  git bisect bad 78aad7f81aa6dfccdb2804ac35db6fc371d265cf
  # good: [356484cabe44984d2dc66a90bd5e3465ba1f64fb] [media] dw2102: resync fifo when demod locks
  git bisect good 356484cabe44984d2dc66a90bd5e3465ba1f64fb
  # good: [e4aa18d33c3a05f9ac51a8c8c7863318c807650f] [media] DocBook: Improve the description of the
  properties API
  git bisect good e4aa18d33c3a05f9ac51a8c8c7863318c807650f
  # good: [e01dfc01914ab9a078ca8d08287c19c6663b5438] [media] videodev2.h: add COLORSPACE_DEFAULT
  git bisect good e01dfc01914ab9a078ca8d08287c19c6663b5438
  # good: [dc9ef7d11207a04514ca195f0c9f4d2ac56696e1] [media] DocBook media: rewrite frontend open/close
  git bisect good dc9ef7d11207a04514ca195f0c9f4d2ac56696e1
  # bad: [5ac417efe66ddd7cd70a98f7f4e32a14ae40a651] [media] sh_vou: avoid going past arrays
  git bisect bad 5ac417efe66ddd7cd70a98f7f4e32a14ae40a651
  # bad: [171fe6d1270d535eae798e4b5acc9f5d25e6e17e] [media] media: davinci_vpfe: set minimum
  required buffers to three
  git bisect bad 171fe6d1270d535eae798e4b5acc9f5d25e6e17e
  # good: [d2b72f6482b9a3c57f036c11786a2489dcc81176] [media] si2168: Implement own I2C adapter locking
  git bisect good d2b72f6482b9a3c57f036c11786a2489dcc81176
  # bad: [694f9963edd831e4ed6fdbcb7134525cf5715a79] [media] media: davinci_vpfe: clear the output_specs
  git bisect bad 694f9963edd831e4ed6fdbcb7134525cf5715a79
  # bad: [2f1ea29fca781b8e6600f3ece1f2dd98ae276294] [media] si2157: implement signal strength stats
  git bisect bad 2f1ea29fca781b8e6600f3ece1f2dd98ae276294
  # first bad commit: [2f1ea29fca781b8e6600f3ece1f2dd98ae276294] [media] si2157: implement signal
  strength stats

  ProblemType: Bug
  DistroRelease: Ubuntu 15.10
  Package: linux-image-4.2.0-23-generic 4.2.0-23.28
  ProcVersionSignature: Ubuntu 4.2.0-23.28-generic 4.2.6
  Uname: Linux 4.2.0-23-generic x86_64
  ApportVersion: 2.19.1-0ubuntu5
  Architecture: amd64
  AudioDevicesInUse: Error: command ['fuser', '-v', '/dev/snd/by-path', '/dev/snd/hwC1D0', '/dev/snd/pcmC1D2c', '/dev/snd/pcmC1D3p', '/dev/snd/pcmC1D0c', '/dev/snd/pcmC1D0p', '/dev/snd/controlC1', '/dev/snd/hwC0D0', '/dev/snd/pcmC0D3p', '/dev/snd/controlC0', '/dev/snd/seq', '/dev/snd/timer'] failed with exit code 1:
  Date: Sat Jan  9 10:53:16 2016
  HibernationDevice: RESUME=UUID=9b9f7b19-cb13-45bc-8d5f-acd5610a93dd
  InstallationDate: Installed on 2014-07-09 (548 days ago)
  InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
  IwConfig:
   eth0      no wireless extensions.
   
   lo        no wireless extensions.
  MachineType: ASUS All Series
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.2.0-23-generic.efi.signed root=UUID=9613d690-85bf-4888-aa33-e0df9be775e7 ro
  PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
  RelatedPackageVersions:
   linux-restricted-modules-4.2.0-23-generic N/A
   linux-backports-modules-4.2.0-23-generic  N/A
   linux-firmware                            1.149.3
  RfKill:
   
  SourcePackage: linux
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 05/15/2015
  dmi.bios.vendor: American Megatrends Inc.
  dmi.bios.version: 2404
  dmi.board.asset.tag: To be filled by O.E.M.
  dmi.board.name: H97M-E
  dmi.board.vendor: ASUSTeK COMPUTER INC.
  dmi.board.version: Rev X.0x
  dmi.chassis.asset.tag: To Be Filled By O.E.M.
  dmi.chassis.type: 3
  dmi.chassis.vendor: To Be Filled By O.E.M.
  dmi.chassis.version: To Be Filled By O.E.M.
  dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2404:bd05/15/2015:svnASUS:pnAllSeries:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnH97M-E:rvrRevX.0x:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
  dmi.product.name: All Series
  dmi.product.version: System Version
  dmi.sys.vendor: ASUS

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