[Bug 1914456] Re: 120 sec kernel timeout is seen during SCSI remove_device.

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: open-iscsi (Ubuntu)
       Status: New => Confirmed

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Title:
  120 sec kernel timeout is seen during SCSI remove_device.

Status in open-iscsi package in Ubuntu:
  Confirmed

Bug description:
  Ubuntu Release
  --------------
  #lsb_release -rd
  Description:    Ubuntu 18.04.5 LTS
  Release:        18.04

  #cat /proc/version_signature
  Ubuntu 4.15.0-122.124-generic 4.15.18

  Package version
  ---------------
  #apt-cache policy open-iscsi
  open-iscsi:
    Installed: 2.0.874-5ubuntu2.10
    Candidate: 2.0.874-5ubuntu2.10

  Problem statement and details
  -----------------------------
  During the automation testing of Cisco's iSCSI target using Open-iscsi initiator, Initiator host reported 120 second kernel hang issue. The automation test was doing SCSI remove_device operation when the issue observered. 
  Automation test perform following sequence of operations,
  1. Establish iSCSI session
  2. Create bunch of iSCSI LUNs.
  3. Discover LUNs through sysfs scan
  4. Format LUNs
  5. Perform IO
  6. Remove LUN
  7. Delete LUN

  Observations from initiator host:
  1. Already discovered iSCSI LUNs went to offline state.
  2. New LUNs are not being discovered.
  3. NOP-in/NOP-out PDU exchange works fine from the iSCSI session.

  Note: Single iSCSI session is present between initiator and target.

  Expected behavior
  -----------------
  SCSI remove_device should succeed and automation test should continue.
  Issue is observed even with following commit, which has fix for similar issue.
  https://kernel.ubuntu.com/git/ubuntu/ubuntu-bionic.git/commit/?id=27dfa4073289ee5737d45b4cfa40b11f5cdeeaa5

  Stack trace
  -----------
  [91832.800739] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  [91832.809982] Call Trace:
  [91832.809994]  __schedule+0x24e/0x880
  [91832.810002]  ? __enqueue_entity+0x5c/0x60
  [91832.810006]  ? select_task_rq_fair+0x642/0xab0
  [91832.810008]  schedule+0x2c/0x80
  [91832.810010]  schedule_preempt_disabled+0xe/0x10
  [91832.810012]  __mutex_lock.isra.5+0x276/0x4e0
  [91832.810017]  ? kernfs_name_hash+0x17/0x80
  [91832.810020]  __mutex_lock_slowpath+0x13/0x20
  [91832.810021]  ? __mutex_lock_slowpath+0x13/0x20
  [91832.810023]  mutex_lock+0x2f/0x40
  [91832.810030]  scsi_remove_device+0x1e/0x40
  [91832.810033]  sdev_store_delete+0x55/0xa0
  [91832.810036]  dev_attr_store+0x1b/0x30
  [91832.810039]  sysfs_kf_write+0x3c/0x50
  [91832.810040]  kernfs_fop_write+0x125/0x1a0
  [91832.810046]  __vfs_write+0x1b/0x40
  [91832.810048]  vfs_write+0xb1/0x1a0
  [91832.810050]  SyS_write+0x5c/0xe0
  [91832.810055]  do_syscall_64+0x73/0x130
  [91832.810058]  entry_SYSCALL_64_after_hwframe+0x41/0xa6

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