SG_IO ioctl issued to a virtio device doesn't finish

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 5 update 7 Beta
  • Architecture: x86_64
  • Kernel Version: 2.6.18-262.el5
  • Drivers or hardware or architecture dependency: virtio,qemu-kvm

Issue

  • With HostOS(RHEL6SP1)/GuestOS(RHEL5SP7 beta), SG_IO ioctl issued to a virtio device doesn't finish.
  • According ot a backtrace, it wait to finish I/O. But this process does not finish
    crash> bt 5785
    PID: 5785   TASK: e74d1000  CPU: 0   COMMAND: "a.out"
     #0 [cfa91ba8] schedule at c061e742
     #1 [cfa91c20] wait_for_completion at c061e8b0
     #2 [cfa91c48] blk_execute_rq at c04e22e5
     #3 [cfa91cd8] sg_io at c04e5e18
     #4 [cfa91d6c] scsi_cmd_ioctl at c04e6347
     #5 [cfa91e0c] blkdev_driver_ioctl at c04e41f4
     #6 [cfa91e28] blkdev_ioctl at c04e490d
     #7 [cfa91f24] block_ioctl at c047ca49
     #8 [cfa91f30] do_ioctl at c048634b
     #9 [cfa91f44] vfs_ioctl at c04868dc
    #10 [cfa91fa0] sys_ioctl at c048697c
    #11 [cfa91fb8] system_call at c0404f44
        EAX: ffffffda  EBX: 00000003  ECX: 00002285  EDX: bfb6439c 
        DS:  007b      ESI: 00a4fca0  ES:  007b      EDI: bfb643dc
        SS:  007b      ESP: bfb64368  EBP: bfb64918
        CS:  0073      EIP: 00289410  ERR: 00000036  EFLAGS: 00000246
  • When they used GuestOS(RHEL6.0), SG_IO run normally.

Resolution

Root Cause

From Technical Notes:

SG_IO ioctls were not implemented correctly in the Red Hat Enterprise
Linux 5 virtio-blk driver. Sending an SG_IO ioctl request to a virtio-blk
disk caused the sending thread to enter an uninterruptible sleep state ("D"
state). With this update, SG_IO ioctls are rejected by the virtio-blk
driver: the ioctl system call will simply return an ENOTTY ("Inappropriate
ioctl for device") error and the thread will continue normally.

Diagnostic Steps

The application starts SG_IO.

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