[Bug 1626737] Re: [4.8.0-14/ppc64el regression] rmmod scsi_debug keeps causing kernel oops

[Brad Figg]

** Changed in: linux (Ubuntu)
   Importance: Undecided => Medium

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Title:
  [4.8.0-14/ppc64el regression] rmmod scsi_debug keeps causing kernel
  oops

Status in linux package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Fix Committed

Bug description:
  Since upgrading to 4.8.0-14, the "storage" autopkgtest of systemd is
  broken. This uses scsi_debug to get a test hard drive, which is reset
  between the test through unloading/reloading the module. This has
  worked fine so far (and still works on amd64/i386), but now regularly
  triggers a kernel oops:

  [  161.120362] Unable to handle kernel paging request for data at address 0x00000000
  [  161.120468] Faulting instruction address: 0xc000000000538ecc
  [  161.120517] Oops: Kernel access of bad area, sig: 11 [#1]
  [  161.120555] SMP NR_CPUS=2048 NUMA pSeries
  [  161.120595] Modules linked in: dm_crypt dm_mod xts algif_skcipher af_alg sd_mod sg xt_TCPMSS xt_tcpudp iptable_mangle ghash_generic gf128mul vmx_crypto virtio_balloon ip_tables x_tables autofs4 ext4 crc16 jbd2 fscrypto mbcache crc32c_generic btrfs xor raid6_pq ohci_pci ehci_pci ohci_hcd virtio_blk virtio_net ehci_hcd usbcore crc32c_vpmsum usb_common virtio_pci virtio_ring virtio [last unloaded: scsi_debug]
  [  161.121016] CPU: 0 PID: 5473 Comm: rmmod Not tainted 4.8.0-15-generic #16-Ubuntu
  [  161.121067] task: c00000005ae51980 task.stack: c00000005ef58000
  [  161.121110] NIP: c000000000538ecc LR: c000000000538ee0 CTR: c0000000000f7250
  [  161.121162] REGS: c00000005ef5b9f0 TRAP: 0300   Not tainted  (4.8.0-15-generic)
  [  161.121213] MSR: 800000010280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 28002444  XER: 20000000
  [  161.121390] CFAR: c00000000009a8e0 DAR: 0000000000000000 DSISR: 40000000 SOFTE: 1 
                 GPR00: c000000000538e98 c00000005ef5bc70 c000000000f67b00 ffffffffffffffff 
                 GPR04: d000000001302018 0000000000000002 0000000000000000 c0000000010d7b00 
                 GPR08: c000000000fa7b00 0000000000000063 0000000000000073 0000000000000004 
                 GPR12: 0000000028002844 c00000000fb80000 0000000000000000 0000000000000000 
                 GPR16: 0000000000000000 00000100331f11f0 00000000384b3890 00000000384b3848 
                 GPR20: 00000000384b3830 00000000384b3870 00000000384b38a8 00000000384b3888 
                 GPR24: 00003fffd23d6e70 c000000000ebdec8 fffffffffffffffe d000000001302018 
                 GPR28: c000000000ebdeb8 0000000000000000 0000000000000000 0000000000000000 
  [  161.122099] NIP [c000000000538ecc] ddebug_remove_module+0x8c/0x160
  [  161.122143] LR [c000000000538ee0] ddebug_remove_module+0xa0/0x160
  [  161.122186] Call Trace:
  [  161.122205] [c00000005ef5bc70] [c000000000538e98] ddebug_remove_module+0x58/0x160 (unreliable)
  [  161.122280] [c00000005ef5bd10] [c00000000018961c] free_module+0x21c/0x3c0
  [  161.122333] [c00000005ef5bd60] [c000000000189a38] SyS_delete_module+0x278/0x2f0
  [  161.122394] [c00000005ef5be30] [c0000000000095e0] system_call+0x38/0x108
  [  161.122445] Instruction dump:
  [  161.122472] 3d42fff5 e92a63b8 7fa9e000 7d3d4b78 ebe90000 419e00bc 7d3e4b78 3b40fffe 
  [  161.122561] 48000018 7fbfe000 7ffdfb78 7ffefb78 <ebff0000> 419e0060 e87e0010 7f64db78 
  [  161.122651] ---[ end trace 5f19b96c7077a0e0 ]---

  This isn't reproducible by merely loading and unloading the module, it
  apparently needs to get some actual exercise. I'll find a simpler
  reproducer than running the systemd test tomorrow morning.

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