[Bug 223381] mpt driver hangs with iscsi devices and scsi drives defined in VBOX FBSD guest

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=223381

--- Comment #8 from Jim D. <randomnoise058 at gmail.com> ---
This bug report is concerned with the hang-/lock-up/freeze of FBSD-11.1 in
VirtualBox where the iSCSI Targets where initially assigned to VBOX SCSI
Contoller (LSIlogic/BUSlogic driver) as noted in the two attachments in the
first comment block. When iSCSI Targets were attached to the VBox SCSI
controller, the FBSD-11.1 VBox guest would freez/lock-up within a handful, or
less, of hours of idle operation with iSCSI Targets attached. It just so
happened that the last system messages were of the "underflow mismatch" type as
noted in Attachement #187481. Also shown in the same attachment is a "vm_fault"
followed by a KDB backtrace output. At this point, the FBSD host was
non-responsive and had to be manually shut down and restarted (ie; pull the
plug).

The first part of my examination of this situation was to attempt to determine
and isolate any command(s) that preceded or induced the "underflow mismatch"
messages. I had completed this exmination in my last/previous comment. Now that
I know what processes were involved with the affected commands, I can isolate
them so that they will not be used, which given everything else in operation,
should prevent the situation that caused the "underflow mismatch" messages.

Since changing the VBox configuration where the iSCSI Targets were moved to the
VBox SATA (ahci) controller - the FBSD-11.1 VBox never locked-up/froze again.
It remained stable over whatever time that it was in operation (> 24 hours).

Looking at the KDB output it is possible that the "mpt" driver is involved.

My next step is to reassign one or more iSCSI Targets BACK to the VBox SCSI
controller WITHOUT the offending smartctl commands and see if anything changes.
Will the FBSD guest still lock-up/freeze without the "underflow mismatch"
messages or not.

The suggestion for suppressing the "underflow mismatch" messages is welcome,
but it is not these messages alone/specfically that this bug report is really
concerned about.

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