[Bug 43085] New: BUG: unable to handle kernel NULL pointer dereference (in scsi_send_eh_cmnd)

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https://bugzilla.kernel.org/show_bug.cgi?id=43085

           Summary: BUG: unable to handle kernel NULL pointer dereference
                    (in scsi_send_eh_cmnd)
           Product: SCSI Drivers
           Version: 2.5
    Kernel Version: 3.4-rc2
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: Other
        AssignedTo: scsi_drivers-other@xxxxxxxxxxxxxxxxxxxx
        ReportedBy: rockorequin@xxxxxxxxxxx
        Regression: Yes


Created an attachment (id=72868)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=72868)
BUG - unable to handle kernel NULL pointer dereference (scsi_send_eh_cmnd)

Whenever I plug my USB3 hub into the PC, I encounter this bug (log attached).
It stops the PC from booting if the hub is inserted at the time, and crashes
USB if I encounter it once the desktop is running.

The line where it crashes is in scsi_error.c at line 782:

struct scsi_driver *sdrv = scsi_cmd_to_driver(scmd);

which expands to:

struct scsi_driver *sdrv *(struct scsi_driver
**)scmd->request->rq_disk->private_data

The issue is that rq_disk is NULL (possibly because it's a USB hub and there
isn't necessarily an underlying hard drive?).

If I make it check for rq_disk being null before trying to assign sdrv and set
sdrv to null accordingly, and then later in the function I check for sdrv being
null before looking at sdrv->eh_action, the error goes away and drives on the
hub seem to mount and function OK (mostly anyway).

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